The attack came inside the clubhouse, while Holm was doing another TV interview.
"I was able to get a hand up and fend off about half of it," said Holm, a Sacramento native who had both his parents and grandparents in the stands.
Holm, who rifled a line drive into the left-field stands, was able to secure the ball in a trade that sent a bat and a helmet to a happy fan.
"[Director of media relations] Blake Rhodes did a great job getting the ball for me," Holm said. "I don't think they would have let me go out there and get it during the game."
Holm was a defensive replacement for Bengie Molina in the seventh inning. He looked like the Giants' home run leader when he hit, too.
"We had to make a move there and take a bat out of the lineup," Giants manager Bruce Bochy said. "Then the kid comes through and hits a big one. It was the perfect time for him getting his first home run."
Even more impressive is that Phillies reliever J.C. Romero, who had allowed one run in his first 15 innings of the season and had not allowed a home run in over 50 innings, was the victim of the blast.
Holm was an unlikely candidate for heroics. He'd never played above the Double-A level until this year, and none of his 29 Minor League home runs were game-winners.
Holm, originally drafted in the 17th round of the 2001 First-Year Player Draft, elected free agency last October but re-signed with the Giants two months later.
"I re-signed with the understanding that I would have a shot at playing in [Triple-A] Fresno," Holm said. "That's all I really wanted. This is as good as it gets."
Holm spent one day in Fresno, and that was an exhibition game in which he played with the parent club, on his way to the big time.
"He did a nice job last year and he did a nice job in the spring," Bochy said. "It wasn't like he was off our radar. We felt he was the best option and he's handled everything we've thrown at him. He looks comfortable out there."
Most of the offensive production came out of the cleanup spot. Molina used a Mother's Day pink bat to single, double and score two runs. He was hit by a pitch in the sixth and Bochy pulled him to put speedster Emmanuel Burriss in to run.
"Down a run, we need to try and tie it," Bochy said. "We have confidence in Holm and that's why we can make a move like that."
Romero retired the first two batters in the seventh before Randy Winn singled into left field. Holm hit the first pitch he saw from the left-hander.
"It was a fastball a little up and I was as aggressive as I can be," Holm said. "That's what they tell you coming off the bench. I didn't know it was out until I reached second base and then I cruised in, making sure not to fall down or do something foolish."
Holm's game-winner was set up by 5 2/3 innings of shutout relief pitching. Billy Sadler, Taschner, Tyler Walker and Brian Wilson combined to keep the Phillies at bay.
"I've been in the situation where I'm warming up in the bullpen and someone hits a home run for the lead before," Walker said. "I had to control the urge to get fired up and excited. You try to think about taking care of business. As a unit, the bullpen pulls for each other. We're in it together. There's a lot of talent in that bullpen."
Sadler retired all five batters he faced, Taschner allowed one hit in the seventh, Walker pitched a perfect eighth and Wilson, who earned his 11th save, gave up a hit but got Jimmy Rollins to hit into a game-ending double play.
"The bullpen saved us," Bochy said. "It started with Sadler. They kept a good offense down and gave us a chance. It would have been frustrating if we didn't win this game with all the chances we had."
Giants starter Jonathan Sanchez struggled for the second straight start, allowing three runs on four hits and matching a season high with five walks in 4 1/3 innings. He also lasted 4 1/3 against the Pittsburgh Pirates last Tuesday.
The Giants won their second straight following a five-game slide.
"It was good to start the homestand off with the series win," Bochy said.