Roger Federer acknowledged he was racked by severe back pain Monday before beating Xavier Malisse 7-6, 6-1, 4-6, 6-3 to reach a 33rd successive grand slam quarter-final.
The six-time Wimbledon champion, who Wednesday faces the Russian 26th seed Mikhail Youzhny for a place in the semi-finals, came from two sets down to defeat France's Julien Benneteau in the last round on Friday.
The 30-year-old Swiss appeared to be in serious trouble again after taking a 4-3 lead in the first set against Malisse, having to leave Centre Court to take a medical timeout.
Painkillers were dispensed to dull the back discomfort.
"I was in a lot of pain," Federer said.
"The treatment and the painkillers worked. I started to feel better as the match went on.
"But it was a shock for it to happen in the first set of a grand slam when you have to play five on grass.
"I thought I was in big trouble at 5-6 and he was serving for the first set. I apologised to Xavier for having to go off. But it was just a freak thing.
"After 15 years on tour if this is the worst it gets, then I'll be happy."
After the medical timeout, Federer stepped gingerly around the court, but having cruised through the first set on a tie-break, the only obstacle he was then facing was the weather.
Rain drove the players off for 40 minutes, although the roof on Centre Court remained open.
Back on court, Federer broke Malisse three times in the second set, taking it 6-1.
The 31-year-old Belgian though hit back to take the third set, but Federer killed off his challenge with two breaks in the fourth set.
Youzhny reached the quarter-finals for the first time with a 6-3, 5-7, 6-4, 6-7, 7-5 win over the unseeded Uzbekistan player Denis Istomin.
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