Andy Murray delighted his tactics paid off against Ivo Karlovic at Wimbledon

Andy Murray found his fourth-round win over Ivo Karlovic "stressful" but believes his tactics proved the difference as the Scot booked his place in the Wimbledon quarter-finals.

Big-serving Karlovic added another 29 aces to his leading tournament tally of 136 but precision conquered power as Murray sealed a 7-6 (9-7) 6-4 5-7 6-4 victory.

It was a tense battle on Centre Court as opportunities to crack Karlovic's serve were few and far between, and Murray had to draw upon all his resilience and returning prowess to seal victory.

The 28-year-old admitted he had to be smart against his 6ft 11in opponent and revealed he made adjustments to his serve to nullify the Croat's booming forehand.

"It's a tactical match, but it's tough. It's quite stressful to play against him," Murray said.

"On this surface, he likes to take chances on the second serve return. It's sometimes maybe the shortest ball or the best ball for him to hit in the rally.

"For him it's right there. He does look to run around and hit forehands. He hits them well. He's a big guy. When he connects with the ball, it's a big shot.

"So I just tried to use some variety there throughout the match to not allow him to be too comfortable. It worked at a few important moments.

"I took a little bit off the first serve. I wasn't serving as hard as usual to try and, again, not allow him the opportunity to go for huge returns or try to come to the net off the second serve return.

"I went for a high percentage of first serves. When I was in the rallies, I felt comfortable."

I just tried to use some variety there throughout the match to not allow him to be too comfortable. It worked at a few important moments.

Pressure game

As well as his thundering serve, Karlovic looked to shorten the rallies as much as possible by rushing to the net and putting Murray under pressure.

Karlovic served and volleyed 101 times in the match, but won only 60 of those points as Murray executed a number of passing shots, and particularly lobs, to great effect.

"If you lob them a few times early in the match, then they can't sort of cheat (by moving) closer to the net when they come forward," Murray said.

"If you see the shot, the volley he missed, at 7-7 in the (first set) tie-break, he actually backed away from the net when I went to hit the passing shot.

"It opens up more angles for you to use when you're passing so it's not like I would just use it against him.

"It's good against guys that come to the net because it stops them from getting too close."

Pospisil next

Murray next faces Canadian Vasek Pospisil, who has never gone past the third round at a Grand Slam before but has capitalised on a kind section of the draw, which saw eighth seed David Ferrer pull out through injury and Rafa Nadal knocked out in round two.

Pospisil, who beat Britain's James Ward earlier in the tournament, has played two five-setters in a row to reach the last eight and Murray believes fatigue could be a factor.

"I think I'm playing well. I'm through into the quarter-finals against Pospisil, which is a good opportunity for me," said Murray, who is yet to lose to Pospisil in three previous meetings.

"I've played him three times on hard courts, I think a couple of them were indoors as well, so I've never played him on grass.

"He's had a good run here and he obviously won the doubles here last year.

"He can play well on the surface. He's also played a lot of tennis here, which is a positive for him in some ways but also maybe he's a little bit fatigued.

"So if that is the case, and I won't bank on that being the case, but if that is the case, I'll try to use that to my advantage.

"Although my match was quite long today, the rallies aren't particularly long, and it's not as physical so I feel pretty fresh."

Shoulder problem

Murray had to take treatment for a shoulder problem in his previous match against Andreas Seppi but the Briton says it has improved.

"It feels better," Murray said.

"I would have liked to have served a little bit bigger today, a little bit harder.

"That's something that as I go on in the tournament, I'll need to try to do more of.

"I'm still conscious of it, I'm playing with quite a lot of taping on the shoulder but obviously I played for three hours today and it feels better than it did three or four days ago, which is positive."