Andy Roddick withstood a fierce onslaught from 12th seed Paradorn Srichaphan to keep alive his Wimbledon dreams with a 6-4, 3-6, 6-3, 6-2 victory in the fourth round on Monday.

The fifth-seeded American had to dig deep for victory and his first Wimbledon quarter-final as the Thai put in an inspired display on Centre Court.

Roddick, who had been broken just once in his first three matches, appeared to be hurtling towards victory as he fired six booming aces on his way to wrapping up the rain-interrupted first set in 23 minutes.

But he came unstuck in the second as Paradorn stunned the bookmakers' favourite with a superb display of power hitting from the baseline.

Having saved numerous break-point opportunities in the first two games of the third, Roddick rediscovered his winning touch to seal the third set with a 199.6 kph ace -- his 11th of the match.

The 20-year-old sealed the win with a fizzing forehand crosscourt winner to set up a last eight meeting with doubles specialist Jonas Bjorkman of Sweden, who beat Belarussian Max Mirnyi 6-4, 3-6, 6-3, 7-6 (7-4).

Swiss fourth seed Roger Federer also marched into the quarter-finals, scoring a straight sets win over Spain's Feliciano Lopez.

The 21-year-old equalled his previous best performance at Wimbledon with a 7-6 (7/5), 6-4, 6-4 victory.

Federer now faces either Rainer Schuettler of Germany or the Netherlands' Sjeng Schalken for a place in the
semi-finals.