The Philadelphia Phillies took advantage, scoring four runs in the ninth inning to beat the Cubs 4-1.
Marmol issued five walks and threw a wild pitch while getting only two outs. Placido Polanco delivered a tying single and Chicago catcher Geovany Soto couldn't hold a strong relay throw to make a tag that would have ended the game.
"Was my responsibility," Marmol said.
Chicago won the first two games of the series and appeared on its way to making it three straight with a 1-0 lead. But pinch-hitters Brian Schneider and Ross Gload worked back-to-back walks with one out in the ninth against Marmol (2-2), who blew his fourth save in 21 chances.
"If he catches the ball, of course Schneider's out. I saw that," Philadelphia manager Charlie Manuel said. "We had a good ninth inning. We caught a couple of breaks there and it went our way."
After Schneider scored, Marmol uncorked a ball-four wild pitch with Jimmy Rollins at the plate as Gload sprinted in with the go-ahead run. After an intentional walk to Ryan Howard loaded the bases, Marmol walked Jayson Werth to force in the third run and was replaced, leaving to boos.
"Sometimes all it takes is one good at-bat, one good hit, one good win to get the team going," said Polanco, just off the disabled list.
"It just fell apart there in the ninth inning with two outs," Cubs manager Lou Piniella said, adding that Soto had plenty of time to tag Schneider but hurried and then didn't hold onto the ball.
"It was a perfect throw. Colvin got the ball in plenty of time and he got a perfect throw and I just plain and simple missed it," Soto said. "I rushed to grab the ball and get a tag and I took my eyes off the ball. ... Nobody is responsible for this game [more] than me."
Marmol had trouble gripping his pitches. But he said the blame was all his.
"I don't make excuses. I walked a couple of guys and that's what happens," he said. "And then a base hit."
Schneider acknowledged he was a bit lucky to get in with the tying run.
"It wasn't that I was slow, he just made a good throw. That's what I'm telling everybody," Schneider said. "It was hit hard, but that was a situation where you have to make them make a perfect throw. He made a good throw, but luckily it bounced off his glove."
As Castro broke for the plate with one out, Theriot dropped down a perfect bunt. Hamels picked up the ball and glanced at the plate, and his throw to first was too late to get Theriot after second baseman Wilson Valdez hesitated and didn't get to the bag in time.
Hamels allowed eight hits in seven innings.
Philadelphia loaded the bases with two outs in the sixth on Werth's double, an intentional walk to Ibanez and another walk to Carlos Ruiz. When Valdez hit a slow grounder to first baseman Derrek Lee, Wells raced to cover and just beat a hustling and sliding Valdez to the bag for the third out.
The Cubs had first and second and none out in the fourth but Hamels escaped, getting Alfonso Soriano to hit into a double play before Castro grounded out. With two runners on in the sixth, Hamels got Soriano to fly out and Soto on a called third strike.
Game-time temperature was 88 degrees. ... Attendance was 40,924.