Trailing, 4-1, in the eighth, Fontenot greeted Ryan Madson with his ninth home run, and first off the bench. Alfonso Soriano doubled and advanced on Ryan Theriot's single to chase Madson. Chad Durbin (5-3) walked Derrek Lee to load the bases for Ramirez, who launched a 1-0 pitch to left-center.
"He likes to be up there in big situations," Piniella said of the Cubs' third baseman. "He knows how to hit and he rises to the occasion. He takes it to another level, and the good ones do that."
Phillies center fielder Shane Victorino didn't move as Ramirez's drive sailed into the bleachers.
"Close game, you just want to put the ball in play," Ramirez said. "I just put a pretty good swing on it."
He came out for a curtain call for the frenzied and very loud crowd of 40,362 at Wrigley Field. Cubs starter Ryan Dempster was in the clubhouse when he heard the fans roar.
"I've said it to many people many a time, Aramis Ramirez is probably ... as clutch a hitter as I've ever seen," Dempster said. "I would say he smells RBIs, especially later in the game. It's something remarkable. It takes a special person to be able to do that, and he does it on a pretty consistent basis, especially if you give him anything to hit."
"I've been able to do that since I was in the Minor Leagues," Ramirez said. "I've always been able to drive in runs. It's something I'm proud of, and I like being in those situations late in the game."
Now one run away from his sixth 100-RBI season in his past eight, Ramirez helped the Cubs improve to 50-19 at home, the most wins at Wrigley Field since winning 51 in 1998. They're the first Major League team to reach 50 "W's" on their home turf. This also was their 38th come-from-behind win.
Fontenot, whom Piniella was hoping would simply get on base to set up the others, was the spark, and Ramirez delivered the knockout punch.
"That's what it's all about, it's about guys picking up each other," Dempster said. "You look at today, Fontenot kind of got that inning started with the pinch-hit home run, it kind of gave us a little bit of energy, and then it was hit, hit and a walk. Next you thing you know, we're up, 6-4. Another big win for us, a big win at home. What a night."
The Phillies were six outs away from moving into a tie for first in the National League East with the Mets when the Cubs rallied. Chicago now has a 6 1/2-game lead in the Central, and is 34 games over .500 for the first time since they ended the 1945 season at 98-56.
Kerry Wood, pitching for the fourth straight day, picked up his 28th save, getting Howard to pop up to Ramirez for the final out. Bob Howry (6-4) notched the win in relief, while Dempster, vying for his career-high 16th win, did not get a decision and was pulled after six innings.
"Stuff-wise, I felt good," Dempster said. "Command-wise, I just wasn't as sharp today. I felt like I was pitching behind in the count a lot. I was able to get out of some jams. Got myself into one in the sixth and didn't manage that inning as well as I probably could have. But that's how it goes, just try to fight my way and keep the game somewhat close. ... I didn't want to let them break it open."
Philadelphia took a 1-0 lead on Victorino's RBI single in the first. Cole Hamels, who held the Cubs to one hit over seven scoreless innings on April 12 in Philadelphia, served up five hits over seven stingy innings on Thursday. The lefty limited the Cubs to two over the first four innings before Kosuke Fukudome singled with one out in the fifth and scored on Mark DeRosa's triple into the right-field corner to tie the game at 1.
The Phillies scored three runs in the sixth, including Carlos Ruiz's tiebreaking RBI single. But the game wasn't over after six.
"We're playing good baseball and we're focused," Piniella said. "We're playing with some confidence. It's a credit to our kids. They don't back off and they keep coming at you and good things happen when you play nine innings of baseball."