ANDY Murray has withstood a titanic challenge from Ivo Karlovic to reach his eighth consecutive Wimbledon quarter-final.

The Scot beat the Croatian 7-6, 6-4, 5-7, 6-4 in three hours and three minutes on Centre Court, and will now meet the unseeded Vasek Pospisil on Wednesday. Pospisil, from Canada, defeated the Serbian No 22 seed, Viktor Troicki, in five sets.

Karlovic, who at 6ft 11 inches is the tallest man ever to have played on the ATP tour, has always been renowned as one of the hardest servers - if not THE hardest - in the game. But, although he is now 36, he has recently added a subtlety and versatility to his game, and at times matched Murray for court craft.

In the end, however, the Scot's ability to return that monstrous serve was crucial. He also successfully employed the tactic - unexpected against such a tall opponent - of lobbing from deep when Karlovic had come into the net.

"I returned his second serve well and I passed well," was Murray's verdict immediately after the match. said. Asked what he expected in the last eight against Pospisil, he added: "After a couple of comebacks he'll be feeling good about his game, so it will be a tough match."

Murray had won all five of his previous meetings with Karlovic, only ever losing a set on a tiebreak. But if anyone thought that simple statistic implied that the Scot would have an easy match, they soon had to think again.

The first ten games all went with serve, although Karlovic had to save a set point in the last of them. Serving again at 6-5 down, he saved three set points with a series if magnificent serves, forcing the set into a tiebreak. He saved two more in that too, before eventually losing the breaker 9-7.

The No 3 seed pressed home his advantage at the start of the second, breaking Karlovic immediately. The older man recovered well from that shaky start, but had to save two more break points at 2-4. At 4-5 behind he served successfully to stay in the set, but then could do nothing to stop Murray taking it in the next game.

From being vulnerable at the start of the second set, Karlovic turned predator at the top of the third, and should have broken Murray for a 3-1 lead. The pressure slowly began to turn on him, however, and he had to pull out all the stops to prevent a break that would have put him 4-3 behind.

Murray then held for 4-4, but a game later found himself serving to stay in the set. His serve had been excellent throughout the regulation 12 games of the first set, and had scarcely dropped off from that high level in the following two sets He kept up that level to close to 5-5, but two games later could not do the same. Karlovic had one break point, and he seized it to take the set.

Karlovic's serve was better by some way in that third set, and at the same time he had cut down significantly on the unforced errors that had dogged him in the first two sets. Buoyed by that improvement, he looked increasingly confident as the fourth set began, and in many rallies had Murray on the back foot. But it was the Scot who had the first break point of the set, in the seventh game, and he got it - although only after he had successfully challenged a ruling that his opponent's shot down the line was in.

Murray had to save two break points himself in the next game before taking it to go 5-3 ahead. Karlovic bravely saved a match point in the following game, but could do nothing to prevent Murray from serving out for the match.