"It's still July," said Sheets (10-4), who surrendered five runs and seven straight hits in the sixth inning alone. "Nobody is winning the Central pennant right now. We don't want to give any of them away, but there is still a lot of season left.
"They outplayed us tonight. I think they outplayed us in every facet of the game, and it started on the mound."
Zambrano (12-4) diced up the Brewers' lineup over eight shutout innings, allowing five singles and two walks while setting a season-high with nine strikeouts. Milwaukee finally collected an extra-base hit in the ninth inning, when Mike Cameron's RBI double off rookie reliever Jeff Samardzija scored Russell Branyan and put the Brewers on the scoreboard.
"When you see a guy like Sheets, you know you have to be almost perfect," said Zambrano, who has allowed one run in 21 innings against Milwaukee this season. "The lineup they have is a pretty good lineup, and you can't make a mistake, and you have to have a pretty good game plan."
But Brewers hitters have been sputtering in the clutch. They were 0-for-5 with runners in scoring position on Tuesday, are 0-for-8 in the series and 3-for-53 (.057) over the past seven games.
After a 7-0 road trip to begin the second half, the Brewers have lost four of five on their homestand.
"The season doesn't stop just because we lost two games to the Cubs," Cameron said.
The Cubs stranded a runner at third base in the first and third innings against Sheets before breaking through in the fourth with Mark DeRosa's sacrifice fly. They piled on in the sixth, collecting seven consecutive hits to open the inning before Sheets finally recorded an out on Alfonso Soriano's sacrifice fly that made it 6-0 and prompted a call for reliever Carlos Villanueva.
Derrek Lee led off the inning with a single and moved to third on an Aramis Ramirez double that banged off the left-field wall, and both runners scored when Kosuke Fukudome's triple bounced past a diving Ryan Braun in left field.
"His only play was to try to dive for it," Brewers manager Ned Yost said. "It was hit in a perfect spot on a perfect line and there was no way he could back up and cut it off. It just piled up on [Sheets]."
DeRosa followed with an RBI single through a drawn-in Brewers infield and Mike Fontenot and Geovany Soto also singled to load the bases for Zambrano. With Brewers infielders again playing shallow, looking for an out at the plate, Zambrano hit a grounder deep to shortstop, where J.J. Hardy fielded it and threw on the run toward home plate. The baseball struck DeRosa on the shoulder and Zambrano was credited with an infield RBI single.
Soriano followed with a deep fly ball to center field to score Fontenot.
Sheets' ERA bumped up above three (to 3.14) for the first time since May 15, when he surrendered a six-run, three-homer seventh inning to the Dodgers.
"Everything [the Cubs] hit didn't go out of the park like in the Dodger game, but it was very similar," Sheets said. "I think you try to prevent a run from scoring and it ends up blowing up in your face. They're going to be better hitters when you're playing [the infield] in, trying to cut off a run. Their average is going to go up."
Sheets set the bar high early this season, going 9-1 with a 2.59 ERA through his first 15 starts. In six starts since, he is 1-3 with a 4.75 ERA.
All indications from Sheets and the Brewers are that the right-hander is physically strong. He has missed parts of every season since 2004 with injuries, but has avoided that bug this year while making his fourth All-Star team.
"There's nothing going on with him," Yost said. "There's nothing actually going on with him. He was pitching really, really well until the sixth inning, his pitch count was down at 75 pitches. Then it just started to pile up on him."
Yost defended his decision to stick with Sheets so deep into the inning. He pulled the plug when Soriano lifted Sheets' 100th pitch for the sacrifice fly.
"When we have one of our two horses on the mound -- CC [Sabathia] or Benny -- I'm going to allow them every opportunity to work through trouble until I feel like the game's gotten by them. That's what we did with Benny, that's what we did with CC [on Monday].
"Ultimately, it's my decision when to pull the plug, but with All-Star pitchers, you have to allow them the ability to work through tough situations, because they have proven to you that they are capable of getting through those situations. They're not going to do it every time, and obviously, Benny couldn't do it tonight."