Czech Radek Stepanek became the first defending champion to lose in the first round of the San Jose Open in 20 years when he was ousted by Belgian Xavier Malisse 6-3, 6-4 on Wednesday.
German fourth seed Tommy Haas was also eliminated, falling 7-6, 6-2 to Uzbekistan's Denis Istomin in the second round of the $531,000 hardcourt tournament.
Third seed Stepanek had four break points against Malisse, but it was the Belgian who made the most of his chances, breaking once in each set to upset the World No 14.
"It's always tough to play the champion of the previous year because obviously they felt pretty good here, and everybody likes the winner of last year," Malisse said.
"I've been injured for a while, so this time I had no pressure on me ... There was nothing to lose."
The victory was the former top 20 player's first on tour since June.
Stepanek had beaten American Mardy Fish for the title last year and was a losing finalist to Andy Roddick in 2008.
Haas failed to convert five break point chances in the opening set of his loss to Istomin, who will play sixth seed Philipp Kohlschreiber in the quarter-finals after the German thrashed Israel's Dudi Sela 6-2, 6-0.
Czech fifth seed Tomas Berdych also made the quarter-finals, posting a 6-3, 6-2 victory over Finland's Jarkko Nieminen.
Andy Roddick brushed off a second set fightback to defeat qualifier Ryler DeHeart 6-1, 7-6 and advance to the second round of the San Jose Open on Wednesday. After breezing through the first set, the big-serving American was broken early to trail 3-0 in the second.
Fellow American DeHeart served for the set at 5-3, but could not close it out as Roddick fought back to force a tie-breaker, then sealed it 7-1 with a forehand winner.
Playing in his first match since the Australian Open, Roddick finished with 11 aces and will next meet Leonardo Mayer in the second round.