The win, coupled with the Mets' 6-1 loss to the Marlins, left Milwaukee one game ahead of New York in the race for the National League Wild Card with two games to play. If New York loses again Saturday and Milwaukee wins behind Ben Sheets, the Brewers' season will stretch into October.
"It's a good feeling when you have destiny in your hands," manager Dale Sveum said. "Now we don't have to chase anybody. We're not tied. It's in our hands now, so we just need to take care of business."
Two slumping Brewers helped put the team over the top. Starter Jeff Suppan remained winless this month but held Chicago to one run in five innings, and right fielder Hart scored one Brewers run and drove in another. He dropped a two-out single in front of left fielder Alfonso Soriano in the sixth inning for a 2-1 lead.
Weeks, who replaced second baseman Ray Durham after Durham re-aggravated a right hamstring strain, provided insurance in the seventh with a three-run home run. McClung (4-4) closed the door by holding the Cubs scoreless on one hit from the sixth inning through the end of the ninth.
The Brewers have won five straight games after a 4-15 start to September turned a 5 1/2-game advantage in the Wild Card standings into a 2 1/2-game deficit.
"I don't even want to think about where we were a week or two days ago," McClung said. "It was like being in detention and we got out for recess. We're getting out there and having fun again."
They also got some help. The Marlins cruised to a win in New York, and that final score drew a standing ovation in Milwaukee when it flashed on the out-of-town scoreboard moments after Weeks hit his 15th home run.
J.J. Hardy was at the plate when the crowd suddenly erupted. In the dugout, Sveum knew what they were cheering for.
"That's one of the better feelings we've all had in the game," Sveum said. "You know that all you have to do is hold a lead and you're going to be one game up for the Wild Card. That's huge."
Suppan went 0-3 with a 10.47 ERA in his first four September starts but returned to his usual late-season form against Chicago, scattering eight hits but limiting the damage to one run in five innings. Brewers center fielder Mike Cameron saved one run -- probably two -- in the top of the first inning with a diving catch that robbed Micah Hoffpauir. Hart and Brewers catcher Jason Kendall teamed up to save another run in the fifth, when Hart's strong throw home froze Mike Fontenot, who had singled earlier, and Kendall fired to second base to catch Hoffpauir trying to take an extra base after he had singled.
The only Cubs run scored came in the top of the second, when center fielder Jim Edmonds hit an opposite-field solo home run. The Brewers answered in the bottom of the inning when Kendall hit an RBI double to the left-field corner off Cubs starter Ryan Dempster.
"It's been a battle for me as of late," Suppan said. "My focus has been the same, it's just that tonight I was able to execute my pitches."
The go-ahead rally came too late for Suppan to improve upon his 10-10 record. Durham led off with a ground-rule double against Cubs reliever Sean Marshall (3-5) and four batters later, with two on and two outs against right-hander Jeff Samardzija, Hart hit a soft single off the end of his bat for the lead.
Hart entered the night hitting .172 in September, but went 2-for-4.
"I had to watch it the whole way," he said of his bloop hit. "That's why I almost missed first base. It's been such a fistfight to get anything done. To be able to come up in that situation, it's nice. When you have any kind of positive, you forget about the bad times a little bit."
"That's Corey at his finest," Sveum said. "That's why it's hard for me to ever substitute for that guy or give him a day off. He seems to do something that helps your team win a ballgame every day, no matter how bad he looks swinging the bat or anything like that."
Sveum said Hart's fifth-inning throw home loomed just as large as his hit in the sixth.
"There's always a turning point in the game, and I think that was it for us," said Sveum, who may have pulled Suppan from the game had Hart not made the play. "That was going to be a tough call for me."
This time, there was no late-inning Cubs comeback. The Brewers had a similar four-run lead in Chicago on Sept. 18, when the Cubs rallied for four runs, all with two outs, and then won the game in the 12th inning. McClung worked two scoreless innings in that game but did not let it get that far Friday.
Sveum, who visited McClung after a two-out walk in the top of the ninth, admitted that he had that game in the back of his mind.
"Unfortunately, there is human nature involved," Sveum said. "It's not like you forget stuff like that. You put it out of your mind, but it keeps you [thinking], 'Hey, this ain't over until the last out is made.' That [Cubs loss] is not too far removed from our season. That was just a week ago that happened."
What a difference that week has made.