Houston:Unseeded Ivo Karlovic of Croatia used his crushing serve to oust German Benjamin Becker 7-5, 7-6 (3) in the first round of the US Clay Court Tennis Championships on Monday.
The tournament also lost its top seed when Andy Roddick withdrew because of a hamstring injury that he "tweaked" again in Davis Cup play last week. Roddick has played in five of the past six finals in Houston and won three of them.
The sixth-seeded Becker took a 2-0 lead in the tiebreaker on consecutive backhand errors before losing six straight points, including an ace from Karlovic. Karlovic won the match three points later on forehand winner.
Karlovic won 73 percent of his first-serve points and had 16 aces.
"Today I was running good and serving well, so I'm pretty happy with the way I played," Karlovic said.
Becker, the 2006 ATP newcomer of the year who ended Andre Agassi's career at the US Open, won only 15 of the 55 first serves Karlovic got in.
The win was Karlovic's second in as many months over Becker. He had 27 aces when he beat the German in the semifinals of SAP Open in San Jose, California in February. Karlovic lost to Andy Murray of Scotland in the final.
Eighth-seeded Juan Monaco, who won his first career title in Buenos Aires in February, put away Jan-Michael Gambill of the United States 7-5, 6-4.
Victor Hanescu of Romania won his first ATP main draw match in more than a year against Martin Verkerk of the Netherlands 6-4, 6-4, and Nicolas Devilder of France beat wild card Justin Gimelstob. of the United States 6-2, 6-3.
Roddick, ranked third in the world, first injured his left hamstring while lunging for a shot in a quarterfinal match in Florida late last month and was forced to retire.
He hurt it again early in his Davis Cup win over Fernando Verdasco of Spain on Friday.
Roddick did not have to play a second singles because the United States clinched the win on Saturday.