Tournament favourite Andy Roddick survived a loss of form to come through a testing match against Paradorn Srichaphan and reach the quarter-finals.
The American number five seed lost his serve for the first time at Wimbledon this year and went off his game for a period in the second and third sets but held on to win 6-4 3-6 6-3 6-2.
Srichaphan, from Thailand, appeared to have Roddick at his mercy for a period in the middle of the match, but grew tired.
And when Srichaphan started to make errors, Roddick broke him twice in the final set to secure the win.
The 20-year-old refused to get carried away afterwards.
"There are eight guys left - I'm just one of them," he said.
"He was hitting the ball very big from the baseline and I had to do something to mix it up."
"He definitely could have taken the match over had he got one of the breaks in the third set.
The American will next play unseeded Swede Jonas Bjorkman, who used all of his experience to beat Max Mirnyi 6-4 3-6 6-3 7-6 (7/4).
Swiss fourth seed Roger Federer had to overcome a potentially serious back injury in his match against Spain's Feliciano Lopez.
The 21-year-old completed a straight sets 7-6 (7/5) 6-4 6-4 win.
But the result masked the difficulty Federer had in disposing an
opponent bidding to become his country's first quarter-finalist at Wimbledon for 31 years.
The Swiss had to come from a break down in each of the first and third sets as his faltering service action gave Lopez hope.
And Federer also had to contend with a back injury, which may jeopardise his future in the tournament.
"I just couldn't move anymore so I had to call the trainer and hope for a wonder," he said afterwards.
"I was always under a lot of pain."
Federer now faces Sjeng Schalken for a place in the semi-finals, after the Dutchman dispatched Rainer Schuettler , of Germany, 7-5 6-4 7-5.
Elesewhere, German Alexander Popp took four sets to beat Belgium's Olivier Rochus 5-7 6-3 6-4 6-2.
And in the day's only unfinished match, Queen's finalist Sebastien Grosjean has a 6-2 4-6 7-6 lead over third seed Juan Carlos Ferrero.