Bowker became the first San Francisco player to homer in his first two games, connecting Sunday in a 7-4 win over the St. Louis Cardinals.
Bowker had an RBI single in the second then homered in the fourth after Bengie Molina reached on an infield single. The ball cleared the 25-foot wall in right field, landing in almost the same spot as his home run on Saturday.
"It's crazy. This is definitely crazy," Bowker said. "I'm having a lot of fun with it. I'm trying to just get good pitches to hit. It hasn't really sunk in."
In two games since being called up, San Francisco's rookie outfielder has provided an offensive spark and added a much-needed power presence in the Giants lineup. He's already second on the team in home runs and RBIs (7) in the first season without Bonds since 1993.
Starter Tim Lincecum, who struck out 11 in six innings, was teammates with Bowker in the minors two years ago and isn't surprised.
"He was doing the same thing so it's nice to see him up here in the limelight doing the same thing," Lincecum said. "It's kind of like he hasn't missed a beat."
Lincecum (2-0) needed 23 pitches to get out of the first inning but settled in after that, allowing just one walk. The 23-year-old righty gave up six hits in six innings and retired 10 of the last 11 he faced.
It marked the third time in 26 career starts that Lincecum has reached double digits in strikeouts, although he wasn't entirely happy.
"You look back at it and it looks good but I always figure there's a couple batters where I could have had a strikeout, or somewhere I got away with pitches," Lincecum said. "So it kind of balances itself out."
Ryan Ludwick homered for the third straight game for the Cardinals and went 2-for-5 with two RBIs.
St. Louis, which rallied from five runs down to beat the Giants 8-7 in 10 innings Saturday, trailed 7-2 but scored twice in the eighth and loaded the bases with two outs against reliever Merkin Valdez before Tyler Walker came in and got Skip Schumaker to ground out to first.
Brian Wilson pitched the ninth to earn his third save in four chances for San Francisco despite giving up back-to-back singles to start the inning. The Giants closer got out of the jam by striking out Ludwick and Chris Duncan before Rico Washington flew out to center to end the game.
Pineiro, the Cardinals' right-hander who began the year on the disabled list due to soreness in his pitching shoulder, looked strong in a minor league start on Tuesday but wasn't nearly as sharp in his return to the St. Louis rotation. He left after giving up six runs and 10 hits in 3 2/3 innings.
"He was in the middle of the plate as he got into it too much," Cardinals manager Tony La Russa said. "The location wasn't good enough and they made him pay."
Bowker's two-run homer provided the big blow off Pineiro (0-1) in the fourth but the Giants strung together five straight hits later in the inning, including an RBI-single by Lincecum and a two-run single from Eugenio Velez.
Bowker added a sacrifice fly in the seventh off St. Louis reliever Ron Villone and was greeted with a standing ovation as he went into the dugout.
"The kid's been a real shot in the arm for us," San Francisco manager Bruce Bochy said. "He came through again today. It's great to have a kid come out here and do what he's doing. We needed some power and he's provided that the last couple of days."
Cardinals 1B Albert Pujols, batting .390 this season, wasn't in the starting lineup but pinch-hit and walked in the eighth. ... St. Louis optioned RHP Kelvin Jimenez to Triple-A Memphis (PCL) to make room for Pineiro. ... Former tennis star Andre Agassi was in attendance with his son and met with several Giants players before the game.