Roger Federer and Novak Djokovic face stern semi-final tests at ATP Finals
Watch Federer vs Alexander Zverev on Saturday from 2pm, before Djokovic vs Kevin Anderson from 8pm, live on Sky Sports Arena.
Last Updated: 17/11/18 4:21pm
Roger Federer and world No 1 Novak Djokovic remain on course to meet in Sunday's ATP Finals showpiece but both players face difficult examinations in the semi-finals.
Federer will continue his quest for a 100th title against Alexander Zverev in the afternoon session from 2pm, while Djokovic will meet Kevin Anderson as the line-up features the top four seeds.
The prestigious season-ending tournament is in its 10th edition at The O2 and there are plenty of thrills and spills in the offing on Saturday, live on Sky Sports Arena.
VOTE: ATP Finals winner 2018
Vote now for the player that you think will come out on top at this year's ATP Finals.
Djokovic, bidding to equal Federer's record of six titles, has looked in imperious form this week - building on the momentum which saw him return to the summit of men's tennis for the first time in two years earlier this month.
Meanwhile, Federer has responded in emphatic fashion to his opening round-robin defeat against Kei Nishikori with back-to-back dominant performances, including victory against the impressive Anderson, to top his group.
Saturday's Order of Play
|Starts at 12pm|| J. Murray (GBR) / B. Soares (BRA) vs  M. Bryan (USA) / J. Sock (USA)|
|Not before 2pm|| R. Federer (SUI) vs  A. Zverev (GER)|
|Not before 6pm|| P.H. Herbert (FRA) / N. Mahut (FRA) vs  J. Cabal (COL) / R. Farah|
|Not before 8pm|| N. Djokovic (SRB) vs  K. Anderson (RSA)|
Despite defeat against Federer, Anderson had already assured his spot in the final four, becoming the first South African through to this stage in the tournament's history - dating back to 1970.
Zverev was the last player to book his spot in the semi-finals after he beat American debutant John Isner in straight sets on Friday.
Here we look ahead to Saturday's two semi-finals at The O2…
Roger Federer vs Alexander Zverev
This promises to be an enthralling encounter. These two met in the round-robin last year, with Federer racing through the final set after tight opening sets.
A major milestone is within Federer's grasp and despite trying to play down expectations this week the 20-time Grand Slam champion will be determined to reach the landmark in London.
Federer admitted he didn't want the feat to "make me go crazy" but with only two wins needed and his performances having improved throughout the week, it would be foolish to rule him out.
Zverev said in his post-match media commitments that he didn't want to feel a sense of satisfaction at having reached the semi-finals for the first time, in only his second appearance.
Did you know...
Alexander Zverev leads the tour with 56 match wins this season.
The 21-year-old, the youngest player to reach this stage since Juan Martin del Potro in 2009, has enjoyed another consistent campaign on tour winning three titles but his hunger for more success is easy to see.
Zverev joined up with Ivan Lendl earlier this summer to help the German make the next step on the Grand Slam stage and at tournaments like this week. It would hard to suggest reaching the last four is not already a sign of progress.
Novak Djokovic vs Kevin Anderson
Djokovic saw his 22-match winning run brought to an end by Karen Khachanov in the Paris Masters final but the Serb has responded this week as you would expect from a champion.
Despite suffering with a lingering cold the 31-year-old produced a masterclass of returning to defeat Isner before winning hard fought first sets against Zverev and Marin Cilic on his way to respective straight set wins.
Djokovic won the event four years in a row between 2012 and 2015 but after missing last year through injury is aiming to complete a remarkable second half to the season with a fifth title.
Anderson has enjoyed a strong debut at The O2, winning his opening two matches, in ruthless fashion but was unable to sustain that against Federer on Thursday.
Having appeared assured on serve, the towering South African saw his serve broken to love in consecutive games by Federer and will now he can't afford a repeat against Djokovic, who prides himself on his returning ability.
The 32-year-old, who reached a career-high of world No 5 after reaching the Wimbledon final this summer, said he failed to adjust to Federer's change of pace and will need to avoid a repeat if he is to cause a shock and reach Sunday's showpiece.
British representation in doubles semi-finals
Jamie Murray and his Brazilian partner Bruno Soares are through to the doubles semi-finals for the third successive year and they will continue their bid for a maiden season-ending title together against American pair Mike Bryan and Jack Sock.
Colombian pair Juan Sebastian Cabal and Robert Farah meet Pierre-Hugues Herbert and Nicolas Mahut in the second semi-final.
Tennis updates straight to your phone
Click here to see how to receive all of the latest tennis news straight to your mobile
We have every major tennis event covered from all angles via our website skysports.com/tennis. On the move? Head to our app for mobile devices and iPad, or follow our Twitter account @SkySportsTennis to join in the conversation.
We will have extensive coverage of the ATP Finals at London's O2 with every match live on Sky Sports. See TV listings HERE.
Keep up to date with the latest on skysports.com/tennis
Well bring you news, previews, live blogs, reports, reaction and expert analysis