Panik, one of eight players the Giants have tried at second, also had an RBI single in San Francisco's four-run rally in the sixth. The rookie is batting .410 (16 for 39) in his last 11 games.
"I feel like I've hit my stride here," Panik said. "When you first come up, everything is new to you. Once I got settled in, I got a feel for everything."
Michael Morse had two doubles and a triple as San Francisco won for the second time in three games following a five-game skid. Blanco went 2 for 2 with two RBIs.
"The bats came to life and we started placing the ball well," Giants manager Bruce Bochy said. "That picks up the energy. It's a great win, particularly after the loss we had last night."
Five San Francisco relievers combined for five scoreless innings after Tim Hudson struggled, giving the Giants time to rally. Jeremy Affledt (3-1) pitched 1 1/3 innings for the win and Sergio Romo got the final two outs for his 23rd save.
Panik led off the eighth with his first career triple and Blanco, who entered as a pinch hitter in the sixth, singled past a drawn-in infield. Antonio Bastardo (5-7) took the loss.
"I got to two strikes and I was just battling," Panik said. "I tried to put a good swing on the ball and I was fortunate enough to hit the gap."
Hudson was charged with five runs and eight hits in four-plus innings.
"I wasn't really in synch," Hudson said.
The Phillies scored three times in the fifth to take a 5-1 lead. Howard had a two-run single against Hudson, improving to .343 (24 for 70) for his career against the right-hander.
Kyle Kendrick pitched five innings for the Phillies, yielding four runs and eight hits.
Buster Posey sparked San Francisco's rally in the sixth with a leadoff single. Pablo Sandoval then hit a high pop fly that dropped between Howard and second baseman Chase Utley. Posey reached second when Utley's backhanded flip took Jimmy Rollins off the base.
"I felt Chase behind me and I heard him say something," Howard said. "All I heard was `Got it.' Talking to him later, he was saying `You got it.' It was a small communication mistake and it started a rally."
Morse doubled home a run and pinch-hitter Adam Duvall drew a walk. Panik and Blanco each followed with soft fly balls that fell in front of outfielders for run-scoring singles.
Phillies: RHP Mike Adams (right labrum fraying) is on a long-toss throwing program. He last pitched in a game on June 6.
Giants: C Hector Sanchez was held out of Friday's rehab game with Triple-A Fresno as he continues his rehab assignment since being cleared to play following a concussion. He was 3 for 18 in his first six games with the Grizzlies.
Phillies: RHP David Buchanan (6-3, 4.40 ERA) makes his third start since returning to the majors for his second stint. After allowing seven home runs in his first five starts, Buchanan has allowed two over his last seven. The Phillies have won eight of their last 13 games at AT&T Park.
Giants: RHP Tim Lincecum (9-8, 4.51 ERA) gets the ball in Sunday's series finale. He is 5-3 in 13 career appearances against the Phillies.
THE KENDRICK FILE
Kendrick can't seem to catch a break when he starts during the day. He left Saturday's game with a lead but ended up with a no-decision and is 1-10 over his last 16 daytime starts.
"He's a competitor," Utley said. "I don't blame him for being frustrated for coming out of the game."
He gave up a first-inning drive by Hunter Pence for the eighth homer he's allowed in the opening frame. He's allowed 25 first-inning runs in his 25 starts.
Kendrick declined comment.