SAN FRANCISCO -- To call Friday's sixth inning a disaster for the Giants would be an overstatement. It wasn't an earthquake, a wildfire or a hurricane.

The inning was, however, a perfect storm of unfortunate circumstances that ruined the Giants' afternoon. The Los Angeles Dodgers scored five unearned runs in the sixth and cruised to a 10-7 victory in the season's first AT&T Park meeting between the archrivals.

Inheriting a 5-3 lead, Osiris Matos (0-1), making his second Major League appearance, allowed all five runs while weathering a succession of four hits. They included run-scoring, two-out doubles by Andre Ethier, Russell Martin and Jeff Kent.

"That's the game," Matos said. "Sometimes everything goes right; sometimes everything goes bad."

Observers might have wondered why manager Bruce Bochy didn't replace Matos with left-hander Alex Hinshaw, who was warming up in the bullpen, particularly when the left-handed-batting Ethier was due up. Disaster -- er, misfortune -- had not yet descended upon the Giants, who led 5-4 at that juncture.

But Bochy wrestled with dual thoughts. First, he needed to conserve his bullpen. Right-hander Keiichi Yabu reported tightness in his shoulder after warming up in the fifth inning, leaving Bochy reluctant to use him. Bochy also wanted to avoid calling upon right-hander Tyler Walker, who was available but still recovering from a mild right inner thigh injury.

Secondly, Bochy believed in Matos.

"I felt he was throwing the ball well," Bochy said. The right-hander had just struck out Matt Kemp for the second out, and the inning's first run scored on what Bochy called a "seeing-eye" single by pinch-hitter Delwyn Young.

So in stayed Matos, and away went the doubles. Ethier's scored a pair of runs, while Martin's and Kent's drove in a run apiece.

If nothing else, the inning was a learning experience for Matos, who finished Thursday's 8-3 victory over Chicago with a scoreless ninth.

"It's hard," he said, describing his brief Major League experience. "You have to make the right pitch."

Bochy came close to second-guessing himself.

"You look back and wish you would have done something a little different there, believe me," he said.

But the Dodgers' uprising partially stemmed from circumstances out of Bochy's control. The inning's first batter, Nomar Garciaparra, lifted a simple fly to left field that Fred Lewis dropped for an error, making all the runs unearned.

Lewis had to charge the ball, but nobody cited that as an excuse.

"He just clanked it," Bochy said. "It was a routine play."

Said Lewis, who was spared another error when he bobbled James Loney's fly ball that center fielder Aaron Rowand barehanded on the warning track, "I just had a bad day today. ... It [the sixth-inning error] cost us the game. I'll come back tomorrow and play harder."

The day began pleasantly enough for the Giants. Rowand, batting .202 since June 3, went 3-for-4 and drove in two runs. Before committing his fielding gaffe, Lewis stroked two hits and, in the third inning, scored on the front end of a double-steal for the second time in four games. They combined for three two-out hits that helped San Francisco build a 5-2 lead through four innings.

But Giants starter Jonathan Sanchez surrendered a leadoff homer to Ethier in the fifth and departed after that inning, having thrown 110 pitches -- which also factored in the bullpen's unraveling. Had Sanchez, who worked at least seven innings in five of his previous six outings, duplicated his recent durability, the relievers would have avoided some duress.

Sanchez explained that he was dropping his arm slightly in his pitching delivery, which elevated his fastball and made it easier to hit. He insisted that the excitement of facing the Dodgers didn't affect him.

"It was just another game," Sanchez said. "A bad game, you know?"

The Dodgers added a run in the eighth on doubles by Martin and Garciaparra, who played his first game since going on the disabled list with a strained left calf on April 26, and another in the ninth on Andy LaRoche's second homer of the season.

Los Angeles' biggest scoring output since May 3 offset a typically plucky Giants effort. Trailing 9-6 in the eighth, San Francisco brought the potential go-ahead run to the plate by loading the bases with nobody out, but Rich Aurilia's double-play grounder dampened the rally.