By JANIE McCAULEY
AP Sports Writer

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.