(CNN) -- Andy Roddick overcame an injury scare to reach the quarterfinals of the SAP Open, but top seed Gael Monfils was forced to pull out of the San Jose tournament with a knee complaint.
Former world No. 1 Roddick had not played since quitting his second-round match at last month's Australian Open, and it looked like another retirement could be on the cards when he rolled his heavily-strapped ankle in the final set against qualifier Denis Kudla.
But second seed Roddick recovered to seal a 7-6 (7-5) 6-7 (5-7) 6-4 victory against the Ukraine-born American on Wednesday and advance to the last eight of a tournament he has won three times.
"I stayed out there and did what I could, and I think he let it get away from him a little bit," the 29-year-old told the ATP Tour's official website. "Probably the best thing I did was exist out there."
Despite his defeat, the 19-year-old Kudla was pleased to go head-to-head with 2003 U.S. Open champion Roddick, now ranked 17th.
"Having to chance to play him was kind of a dream come true at first," said Kudla, who will break into the world's top 200 for the first time next week.
"Obviously when I got on court, it's business, you've got to go out there and win, but it's great to be able to play him."
Roddick, seeking his 31st ATP Tour title, will play either Uzbekistan's Denis Istomin or fellow American Michael Russell for a place in the semifinals.
But world No. 13 Monfils will play no part in the event, and has also pulled out of next week's event in Memphis -- an indoor hard-court tournament Roddick has won twice in the last three years.
American "lucky loser" Blake Strode will take the Frenchman's place in Thursday's second-round clash with Bulgarian qualifier Dimitar Kutrovsky.
Defending SAP Open champion Milos Raonic beat his predecessor as ATP Newcomer of the Year, Tobias Kamke of Germany, to reach the quarterfinals.
Canada's Raonic, who claimed his first ATP title at the 2011 tournament, found himself 1-5 down in the second set, but recovered to seal a 6-2 7-6 (9-7) win late into the night.
At the World Tennis Tournament in the Dutch city of Rotterdam, Argentinian third seed Juan Martin Del Potro -- the 2009 U.S. Open champion -- beat Slovakian Karol Beck 6-4 7-5 to reach the last eight.
He was joined by the Czech Republic's Tomas Berdych after the second seed's opponent, Marcos Baghdatis, retired hurt with a foot injury in the first set.
Frenchman Richard Gasquet, seeded five, defeated Russian Alex Bogomolov Jr. 6-3 6-2 to book his place in the quarterfinals.