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Dementieva: Nervy win.
1658 Giant-killer Zheng, who put out world No1 Ana Ivanovic earlier in the tournamant, serves out to win the final set 6-1 and a topsy-turvy match to set up a semi-final showdown with Serena Williams.
1655 Winner from Zheng and she serves for the match with a double-break in hand.
1654 Third break point for Zheng who is always in charge if the rally goes beyond four strokes.
1652 Zheng has a break point for a 5-1 lead but Vaidisova holds her off for the moment.
1650 Serena cruises into the semi-finals whizzing through the second set without losing a game and toppling Radwanska in just 53 minutes.
1648 Radwanska looking frustrated as Serena's power takes her to a 5-0 second-set lead.
1647 A solid service game from Zheng and she takes a 4-1 lead.
1645 Another string of unforced errors allows Zheng to break and go 3-1 ahead in the deciding set.
1644 Serena now motoring through the second set and 4-0 up.
1643 Good serving and a spectacular drive volley helps Vaidisova to 40-15.
1641 A double on break point and Radwanska pays the penalty going 3-0 down to Serena.
1640 Vaidisova goes 30-15 ahead on Zheng's serve but the Chinese woman battles back to make it 2-1.
1638 Vaidisova holds on to level at 1-1 and a thrilling final set is on the cards.
1637 Comfortable service game for Serena and only a remarkable turnaround can stop her reaching the sem-finals.
1634 A break straightaway for Serena and Radwanska's chances are now slowly fading.
1633 Zheng takes the opening service game in the final set but it's a tense affair going to two deuces.
1630 Serena too strong on serve and her blistering forehand and takes the first set 6-4.
1628 Zheng puts a crucial volley out and Vaidisova holds on to take the second set 7-5 and it's a set apiece and it's difficult to call a winner from here.
1627 Battling effort from Radwanska holds onto her service game and it's 5-4 now.
1626 Vaidisova goes 30-love head but Zheng hits back with some brilliant shots to grab a break point.
1624 Serena is moving through the gears and eases into a 5-3 lead in the opening set.
1623 Wild volley from Zheng and Vaidisova gets the break to go 6-5 ahead and now serves to level the match.
1622 Superb returns from Vaidisova gives her three break points.
1621 Serena now steps up a gear to break Radwanska to 15 and assumes control of the set again.
1620 Big serving from Vaidisova helps her avoid defeat and it's now 5-5.
1618 Serena gets her serve going again and holds to level the set up at 3-3.
1616 Zheng cruises through her service game and is now one game away from a semi-final spot.
1614 Radwanska holds onto her serve with some enterprising play and holds an early lead.
1613 Vaidisova levels at 4-4 and the second set is heading to a tense conclusion.
1612 Serena is broken thanks to some consistent hitting from her opponent.
1611 Break point for Radwanska to level the match with Serena in two minds about coming into the net.
1610 Vaidisova earns hersel;f a break point with her potent double-handed backhand but Zheng produces two wonder shots to hold onto her serve.
1608 Zheng shows no signs of capitulating and breaks back immediately.
1607 A break for Serena thanks to her powerful groundstrokes.
1606 Brilliant rally with Serena chasing lost causes and Radwanska commanding at the net before coming up with the winning volley.
1604 Despite having her left thigh heavily strapped, she gives Serena a few scares before the first set is levelled at 1-1.
1602 Solid opening game from Radwanska and she takes first blood.
1601 Zheng is broken by a very deep return from Vaidisova who now gets the first break in the second set.
1557 Vaidisova is made to work hard again to win her service game but levels the set up at 2-2.
1554 Serena Williams comes onto court to meet Agnieszka Radwanska in the last of today's quarter-finals.
1553 Zheng wins the next game to love and still looks well in control.
1551 Vaidisova is hitting the lines to level at 1-1 but she needs to because Zheng is punishing anything in open court.
1547 Vaidisova's ground strokes are putting Zheng under pressure but she throws in a wild one when she needs it most and Zheng holds on to a tense first game in the second set.
1544 She's done it!! After the best part of two and a half hours, Dementieva needs only one more match point to close out the game and now meets Venus Williams in Thursday's semi-final.
1543 Crunch time for Dementieva serving for the set and holding it together to lead 30-15.
1541 Zheng closes out the opening set and looks well in control at the moment.
1540 A couple of big serves from Petrova saves the day and it's back to 5-3.
1539 Unforced errors from Petrova and Dementieva in sight of victory again.
1536 Zheng hits the ball incredibly powerfully fro someone of her stature and she holds all the aces in the opening set at 5-2.
1535 More doubles from Dementieva but wild forehands from Petrova help her out and the lead is now 5-2.
1533 Dementieva wastes both chances and Petrova holds on to reduce the gap to 4-2.
1530 Now it's Petrova's serve to come under pressure as Dementieva rushes the net and takes the point to secure two break points.
1528 Vaidisova converts the second one and is how only 4-2 down with her serve to come.
1527 Vaidisova has two more break points in game five but can she take advantage?
1526 A double from Dementieva on break point and Petrova is back in it at 4-1. Is another crazy collapse on the cards?
1524 Petrova is turning on the power and pegs back Dementieva from 40-15 to deuce.
1520 Another break for Dementieva aided by a double by Petrova at 30-all and surely Dementieva cannot waste this double break?
1518 Vaidisova wastes two break point chances and alllows Zheng to go 3-0 ahead.
1515 Flying start by Zheng as she breaks Vaidisova in her opponent's opening service game.
1514 The real Dementieva is back on court dominating the game with powerful groundstrokes and building up a 3-0 lead.
1511 Break for Dementieva thanks to some fragile serving by Petrova and good returns by a resurgent Dementieva.
1509 Petrova's serve now under pressure at 15-30 after a double and a woefully short second serve.
1506 Dementieva takes the opening game of the final set but her crumbly serve is put under pressure again by Petrova, who takes the game to deuce before losing.
1503 Vaidisova and Zheng about to get under way on Court 1.
1458 Phenomenal rally again and Petrova comes out on top as she forces Dementieva wide before dropping a volley into the open court. We are into an unlikely third set.
1457 A long rally is won again by Petrova and now she has a set point.
1455 Demetieva then loops a return long and Petrova is now 6-6 with her in the tiebreak.
1454 It has been a battle but Dementieva has two match points - Petrova manages to save the first.
1450 It is all over Court 1 as Venus dominates the final rally and secures victory on her first match point 6-4 6-3. Jie Zheng and Nicole Vaidisova will be up next.
1449 A fine forehand return from Venus sets up two match points for Venus.
1447 Dementeiva holds in the 12th game of the second set to force a tiebreak.
1445 Tanasugarn continues to fight like a tiger but but Venus is able to just draw ona big serve or two when it counts. The Thai is now serving to stay in the match.
1441 Amazingly Petrova now leads 6-5 after holding her own serve. Tanasugarn also holds on Court 1 to stay just a break down at 3-4 in the second set against Venus.
1438 Petrova has come back from nowhere and breaks Dementieva yet again to tie up the second set at 5-5.
1437 Venus holds her service and leads 4-2.
1436 Venus is just too strong and saves both the break points.
1435 Chance for Tanasugarn - two break points against Venus.
1433 Petrova closes to 5-4 but once again Dementieva has the chance to reach the last four on her own service.
1431 Tanasugarn holds once again in battling fashion and now trails 2-3, a break down to Venus.
1429 Tremendous rally on Court 1 on break point to Venus but she comes in to kill the rally only to see her forehand fail to clear the net.
1428 Petrova takes advantage and cuts the deficit in the secod set to 5-3.
1427 Some wayward shots from Dementieva as she tries to serve out sees Petrova have a break point.
1423 Venus is finding her range with the serve now and two aces wrap up a convincing game and see her lead go to 3-1.
1422 Petrova clinging by a thread but manages to hold serve and trails 5-2 in the second set.
1421 Tanasugarn does get under way in the second set and scrambles to a winning service game - she now trails 2-1 and is a break down.
1417 Venus breezes through her service game to love and goes 2-0 up in the second set.
1415 Venus gets that early break on Court 1 and it could be a long way back for Tanasugarn while Dementieva holds to get on the brink of victory at 5-1.
1414 Not good from the Thai and Venus has two early break points while Demetieva is now 4-1 up on Centre as she breaks Petrova again.
1412 Tanasugarn serves first in the second set and it is vital that she gets a game on the board.
1411 Dementieva still stays in command on Centre and now leads 3-1.
1410 Venus finally prevails and she takes the first set 6-4 although clearly not anywhere near her best.
1408 Another unforced error sees Venus slam the ball into the net and Tanasugarn is still alive in the set at deuce.
1407 Accurate drive volley from Venus sets up a set point.
1406 Petrova finally stops the rot and gets on the scoreboard at 2-1 in the second set.
1404 Lucky netcord for Tanasugarn makes it 30-30 in the 10th game. She then lobs Venus to set up a vital break point.
1401 Tanasugarn has to battle hard once again but she holds and will at least make Venus serve for the first set.
1358 Petrova clearly frsustrated with her game today and has a little throw of the racquet on the baseline.
1356 Petrova can't get going and Dementieva breaks to win the first game of the second set.
1353 Venus wins her next service game to love and Tanasugarn will have to hold to stay in the first set.
1349 Tanasugarn holds on to close the deficit to 4-3. Dementieva wraps up the opening set on Centre with a 6-1 scoreline over Petrova.
1348 Tanasugarn sticks in well though to save it and makes it deuce.
1347 Venus has not played well but she has break point for a 5-2 lead.
1346 There is another break on Centre for Dementieva and she leads 5-1 and will serve for the first set.
1344 Venus picks the right time to unleash two big serves and she finally holds. She leads 4-2.
1343 Dementieva is on top against Petrova and leads 4-1 while Tanasugarn lets another break point slip by.
1342 The next break point is up straight away but Venus finds her range on first serve and rescues the situation.
1341 She has every chance on the Williams second serve but her return goes long. Bit of a waste.
1340 A rasping winner down the line sets up Tanasugarn with another break point.
1338 Noticeable that Venus is struggling with her serve although Tanasugarn can't convert a break point.
1337 Dementieva gets the break and now leads 3-1.
1335 Dementieva holds and leads 2-1 on Centre. She then has three break points on Petrova's next serve.
1332 It is an erratic start on Court 1 as Venus races to 40-0 on Tanasugarn's next serve and then comfortably converts her first break point. Venus leads 3-2.
1330 Venus hits a return long and the Thai immediately breaks back to make it 2-2.
1328 Some booming groundstrokes from the back of the court by Tanasugarn has Venus on the back foot and the Thai has a break point.
1326 There is a break point for Petrova on Centre but a wide return means she can't take advantage.
1324 Venus has the early edge and breaks Tanasugarn to 30 to lead 2-1.
1323 Petrova, who's right knee is quite heavily strapped, has to dig in but holds and makes it 1-1.
1321 Venus sluices through her first service game and levels things up at 1-1.
1320 Petrova comes back from 0-40 on her first service game to level things at deuce.
1317 Pretty convincing opening service game from the Thai player while Dementieva saves a couple of break points against Petrova to hold serve in their opening game.
1315 Tanasugarn will serve first and wins her opening point.
1310 We will keep you up to date with the action on Centre but our focus will be on defending champion Venus. Any thoughts then email in to david.john@bskyb.com.
1308 Dementieva warms up with a few serves on Centre Court.
1304 Venus Williams and Tamarine Tanasugarn are just being given instructions from the umpire on Court 1 and now get ready to warm up.
1300 It won't be long before the players emerge for the first two women's quarter-finals and the scene could not be better with perfect weather.
1218 The action is under way on the outside courts with plenty of doubles matches and more from the boys's and girl's singles.
1155 Welcome to Tuesday's action at SW19! The women are the focus with four quarter-finals taking place today - Elena Dementieva is the highest-seeded player still in the tournament and she is first up on Centre Court where she faces Nadia Petrova.
