AT&T PARK
FINAL
1 2 3 4 5 6 7 8 9 10
PADRES
0 1 0 1 0 0 1 1 0  
GIANTS
1 1 0 1 0 0 0 0 0  
R H E
4 10 0
3 9 0
WINNING PITCHER
Gregerson
#57 RHP
1-3, 3.03 ERA
0.1 Innings
0 ER
LOSING PITCHER
Affeldt J. Affeldt
#41 LHP
1-2, 1.89 ERA
1.0 Innings
1 ER

SAN FRANCISCO(AP) The San Francisco Giants need injured ace Tim Lincecum down the stretch. His replacement wasn't half bad.

Chase Headley homered and singled in the go-ahead run in the eighth inning as the San Diego Padres spoiled an impressive major league debut by San Francisco starter Madison Bumgarner with a 4-3 victory Tuesday night.

San Francisco fell three games behind Colorado in the NL wild-card race after the Rockies beat Cincinnati 3-1.

''We need to get (Lincecum) out there on the mound,'' catcher Bengie Molina said. ''Very tough. Any time you lose at this stage, at this time, it's going to be a tough loss.''

Will Venable hit a tying solo homer in the sixth and Kevin Kouzmanoff also connected for the Padres, who won in the Giants' waterfront ballpark for only the second time in eight games this year.

Luke Gregerson (1-3) recorded the final out of the seventh for his first major league win. Heath Bell pitched the ninth for his 36th save in 39 chances.

Headley singled against Jeremy Affeldt (1-2), who hadn't allowed a run in seven outings and 10 of his last 12.

Bumgarner was called up from Double-A Connecticut and pitched in place of Lincecum. The reigning NL Cy Young Award winner is nursing inflammation in his back and the Giants expect him to make his next turn in the rotation.

''There's a part of me that likes seeing the best pitchers in the game pitch,'' Padres manager Bud Black said, referring to Lincecum's absence. ''We've been playing pretty good ball the last six weeks. It's sort of been a trend of this club all year. Our guys keep it going during the course of the game. We're pesky.''

Bumgarner, an imposing left-hander, walked off to a standing ovation and tipped his cap to the crowd after giving way to Brandon Medders with one out in the sixth.

''It took about 'til the fifth inning for the nerves to wear off,'' Bumgarner said. ''I just made some bad pitches. They'll take advantage more than in the minor leagues. A lot better hitters for sure.''

Bumgarner gave up the two homers for his lone runs. He struck out four and walked one, throwing 76 pitches and 48 for strikes.

He knelt down moments before throwing his first pitch, then received a quick pep talk from second baseman Freddy Sanchez . Bumgarner threw a 91 mph strike on his first pitch then got Everth Cabrera on a comebacker on a full count for the first out.

Kouzmanoff's drive leading off the fourth tied the game at 2, then Eugenio Velez 's infield single in the bottom half put San Francisco ahead. Venable's homer in the seventh made it 3-3.

Kouzmanoff later left the game with a strained left calf.

The 20-year-old Bumgarner has made a rapid ascent through the farm system, similar to that of Lincecum, who was the 10th pick in the 2006 draft. Lincecum spent just one full season in the minors before being called up in 2007.

Bumgarner found out about 3 1/2 hours before the first pitch from manager Bruce Bochy that he would be starting and did some last-minute preparation with Molina and pitching coach Dave Righetti .

''He showed good poise out there,'' Bochy said. ''He didn't get rattled after the home runs and came back and made pitches.''

Bumgarner - who thought he would be pitching Wednesday in the Double-A playoffs - got the call Monday that he was coming to San Francisco. His fiancee, Ali Saunders, flew to the Bay Area from North Carolina on Tuesday to join him.

He was a combined 12-2 between Double-A Connecticut and Class-A San Jose this season and had gone 5-0 since his lone loss for Connecticut on June 13.

One fan wearing Lincecum's No. 55 jersey taped a piece of paper with Bumgarner's name over Lincecum.

''It's an honor they know who you are,'' Bumgarner said.

At 20 years and 38 days, Bumgarner became the fourth-youngest San Francisco pitcher to make his big league debut and the second-youngest in franchise history to start behind Mike McCormick , who was 17 years, 342 days when he debuted in 1956.

Former Giant Kevin Correia struck out five in six solid innings but didn't get a decision after winning his two previous starts.

NOTES: The Padres are 24-16 since July 28. ... San Diego leads the season series 8-6. ... San Diego is giving its starters an extra day and RHP Edward Mujica will make a spot start at home Friday vs. Colorado. ... The Padres recalled LHPs Aaron Poreda and Cesar Ramos from Triple-A Portland. Now, San Diego has three of the four players up who the Padres received in the trading deadline deal with Chicago that sent 2007 NY Cy Young Award winner Jake Peavy to the White Sox .