By Mitch Phillips

LONDON (Reuters) - Home hope Andy Murray battled through to the last 16 at Wimbledon with a nervy 6-4 4-6 6-1 7-6 win over imposing Croatian Ivan Ljubicic under the Center Court roof on Friday.

The fourth seed, bidding to become the first British men's singles champion at Wimbledon for 75 years, looked edgy for long spells against the former world number three.

Without ever looking totally at ease he eventually came through another testing encounter. However, he and the three big guns seeded above him, know he will need to find more aggression in his play and more control of his emotions if he is to go on and land the ultimate prize.

"It's still very intense, I felt like I played good tennis from the back of the court and moved well but I just need to serve better," Murray said in a televised interview.

The players had met six times previously and were level at three victories apiece, the Croat winning their most recent clash in Beijing last year.

Having the roof closed does make the atmosphere more akin to an indoor tournament but Murray, who has now played three full matches under it, including his first here on Monday, knows the conditions better than anyone.

He looked off beam in the early stages on Friday, however, and Ljubicic, a former French Open semi-finalist, silenced the home crowd when he broke to love in the seventh game.

Murray, as so often before, seemed to need a scare to shake him into action and he duly roared back by winning the next three games in a row, two against serve, to chalk up the first set.

With all the other courts rained off, all eyes were on Murray - in Center Court, on screens around the complex and live on prime-time TV.

But he made the fans suffer by delivering an appalling service game to open the second set as he beat himself into a frenzy of frustration, screaming at every error and drumming his racket into the innocent turf.

When he won the Queen's tournament two weeks ago Murray said he had benefitted from his new calm approach but there was little sign of it on Friday and his lack of control and some sustained hitting by Ljubicic gave the Croat the second set.

On Monday Murray lost the first set and was 3-3 in the second against Spaniard Daniel Gimeno-Traver but won 15 games in a row to quickly turn things round.

He was not quite so dominant this time but the third set was a one-sided affair that calmed him down and got the crowd firing again.

Ljubicic, 32-years-old and weighing in at 14 stone 7lbs (91kg), began to look weary and though he was still pounding down some heavy serves, Murray became more aggressive with his returns and duly broke in the fifth game.

Murray managed to lose his serve while serving for the match at 5-4 but went on to take the nervy, late-night tiebreak 7-4 and earn himself the weekend off.

"When I served for the match he swung and made it," Murray, who performed one of his now signature between the legs shots, said. "You'll have tough sets and you have to come through tough matches in grand slams and the matches are going to get tougher."

(Editing by Ed Osmond)