Andy Murray is safely through to another Wimbledon quarter-final but insists his path to the final is by no means guaranteed.

After the shocks and injuries of the early few days that claimed Roger Federer, Rafael Nadal, Maria Sharapova and Victoria Azarenka, there was arguably the biggest upset of the lot yesterday when Serena Williams lost to Sabine Lisicki.

Williams had not lost a match since February, a run of 34 contests, and the Centre Court crowd was still stunned by what they had just witnessed when Murray and Mikhail Youzhny walked out.

There was a palpable sense of anxiety for the home favourite, and he wobbled in the second set before coming through 6-4 7-6 (7/5) 6-1 to make a sixth successive Wimbledon quarter-final.

Despite the unpredictability of the tournament, it would be a surprise if the men's final did not feature Murray and Novak Djokovic, but Murray said: "When someone like Serena loses, she hasn't lost for a long time.

"So for her to lose at Wimbledon in the fourth round, especially a match where she'd come back, had a lot of chances, it's surprising.

"When those sort of results can happen to a player as good as her, there's absolutely no reason why it can't happen to me. That's why I'm not getting ahead of myself, and no one else should."

Murray was not as fluent as he had been in his first three matches and had to come from 5-2 down and then 5-3 in the tie-break to win the second set, yelling and pumping his fist as a backhand return fizzed past Youzhny on his first set point.

The Scot clutched at his side a few times during the match, which was a worrying echo of his back troubles during the clay-court season that ended with him pulling out of the French Open.

He played down worries over his fitness, though, saying: "There's no cause for concern. My back is what it is. It's felt way, way better than it was a few weeks ago.

"There's a few times on the court where you feel things. You just have to find a way of managing those issues and getting through them because a lot of guys have had problems during this slam especially.

"A lot of guys have had trainers on court and whatnot. So everyone's got little niggles. You just have to manage them and get through it."

And Murray assured British fans something drastic would have to happen before he joined the long list of withdrawals from the tournament.

The second seed, who next meets Spain's Fernando Verdasco, said: "Now that I'm playing, there's no chance I would stop unless I couldn't hold the racket."