MILWAUKEE — With the postseason approaching, Jason Hammel is hurting his chances of claiming a spot in Chicago’s playoff rotation.

Hammel surrendered five runs in the first inning and ended up allowing nine runs — eight earned — over 5 2/3 innings in the Chicago Cubs’ 12-5 loss to the Milwaukee Brewers on Tuesday night.

“Just too many pitches up in the zone,” Hammel said. “I didn’t really set the tone for us early. This one is on me. Obviously, it doesn’t sit well, but we’re fortunate to have a very comfortable lead right now. I’ll just brush this one off and move on.”

The NL Central-leading Cubs had won seven of eight and were 41 games over .500 after winning Monday’s series opener.

But Milwaukee rallied from a 1-0 deficit as its first seven batters reached against Hammel (14-8). Jonathan Villar homered on Hammel’s second pitch, Ryan Braun had an RBI single, Domingo Santana singled in two runs and Martin Maldonado added a sacrifice fly.

Hammel allowed more runs to the Brewers in the first inning Tuesday than he had in any of his 14 previous career outings against them — the right-hander entered 10-1 with a 2.50 ERA against Milwaukee.

“We haven’t had a first inning like that,” Brewers manager Craig Counsell said. “He’s been tough against us. You get to him before they get in that rhythm and take advantage of it.”

Hammel has a 9.35 ERA over his past four starts, a stretch that also includes an outing against Pittsburgh on Aug. 31 in which he gave up one run over six innings.

“I just haven’t had a good feel for my slider over the last few,” Hammel said. “I’m just trying to feel it right now. I had a good curveball today, but not having that slider, that’s usually my pitch when I’m behind in the counts.”

After allowing five runs in the first, Hammel allowed just an unearned run over the next four innings before giving up the three-run home run to Ryan Braun in the sixth.

“Usually if they are going to get him it is going to be early in the game,” Cubs manager Joe Maddon said. “When he gets deeper into the game he usually settles in. I thought he did settle in. Obviously, the three looks bad at the end.”

Chicago scored four of its five runs on home runs.

Anthony Rizzo hit a solo home run to give the Cubs a 1-0 lead in the first and a two-run shot in the eighth that chased starter Wily Peralta. Miguel Montero hit a solo shot in the second inning.

Peralta retired 11 straight Cubs after allowing a one-out single to Ben Zobrist in the third, a run that was snapped by Tommy La Stella’s double in the seventh.

“We couldn’t muster any offense,” Maddon said. “Peralta pitched well in his last game and did pretty well again today.”

FAMILIAR FOE

Rizzo is 16 for 32 with seven homers and 14 RBIs against Peralta.

“I’m going to try to find a way to get him out,” Peralta said. “I feel like I made two good pitches to him. You have to tip your hat to him. He’s been killing me.”

TRAINER’S ROOM

Cubs: Activated from the disabled list prior to Tuesday’s game, RHP Hector Rondon allowed a run in his first inning since Aug. 16.

UP NEXT

Cubs: LHP Mike Montgomery (1-1, 4.09 ERA) will start the series finale against the Brewers. He has a 4.01 ERA in five starts and a 2.29 ERA in 37 relief appearances for Seattle and Chicago this season.

Brewers: RHP Matt Garza (5-6, 4.57) will pitch against his former team for the second time this season. He has allowed just one earned run over 12 1/3 innings in his past two starts.