SAN DIEGO (AP) -- One bad start down, six more chances for Brandon Webb to get 20 wins.
Webb got knocked around in one of his worst starts of the season as the San Diego Padres denied him becoming the majors' first 20-game winner with a 9-2 victory over the Arizona Diamondbacks on Tuesday night.
Webb (19-5) lost in his first bid to become the NL's first 20-game winner since 2005 with one of his few bad outings, allowing six runs and nine hits in 4 2/3 innings.
"Pretty much from the get-go I didn't have my good stuff," Webb said. "I couldn't get ahead. My curveball and changeup weren't really there. Overall, not a very good night."
It marked just the fourth time in 28 starts that the normally consistent Webb did not pitch at least six innings. The right-hander had his shortest outing in 13 starts, since he lasted 3 1/3 innings in a 15-1 loss at Oakland on June 4.
"Right when I got out there, I knew something wasn't right," said Webb, who lost for the first time in nine decisions. "I was struggling to get ahead. It was just brutal."
Webb, the 2006 NL Cy Young Award winner, figures to get at least six more starts in Arizona's final 30 games.
"That was very atypical," Diamondbacks manager Bob Melvin said. "You don't see that too often."
Giles hit a three-run homer and Kouzmanoff added a two-run double in a five-run third inning as Arizona lost its third straight and fourth in five games. Kouzmanoff added an RBI double in the seventh.
The Diamondbacks retained their three-game lead over the Los Angeles Dodgers in the NL West.
"I think he probably didn't have his best stuff," Giles said. "But even when he doesn't have his best stuff, he's got quality stuff to get you out. We did a good job of waiting him out and getting balls that were up in the zone."
Rookie Chad Reineke (2-1) pitched five innings for the win and combined with five relievers on a three-hitter.
Giles hit his 10th home run with one out in the third after singles by Nick Hundley and Tadahito Iguchi for a 3-0 lead. After a single by Luis Rodriguez and a two-out walk to Adrian Gonzalez, Kouzmanoff doubled in both runs.
"That was a very good inning against a guy who looks like he's on his way to the Cy Young," Padres manager Bud Black said.
"With Brandon, you have to be patient because he sinks the ball and tries to get you to chase his off speed stuff," Kouzmanoff said.
Mark Reynolds hit a two-run homer, his 25th, with two outs in the fourth off Reineke, but the Diamondbacks could manage little else.
"We had some shots against [Reineke]," Melvin said. "We just couldn't get the big hit."
Reineke gave up two runs and two hits in his third major-league start.
Webb won both previous starts against San Diego this season without allowing an earned run in 13 innings, including a 4-1 win in Arizona on Thursday.
"I knew what to do to fix the problem, but I couldn't do it," Webb said. "That made it frustrating."
The Padres won a home series for the first time since winning two of three against the Dodgers, June 10-12. San Diego, which won the first two games of the three-game set against Arizona, broke a string of nine straight losing homes series.
The NL has not had a 20-game winner since St. Louis' Chris Carpenter, Florida's Dontrelle Willis and Houston's Roy Oswalt in 2005. ... Webb's ERA rose from 2.74 to 2.96. ... Arizona's Adam Dunn walked three times to raise his major league-leading total to 99.