For the second straight game, a St. Louis Cardinals starting pitcher was rocked after getting extra rest. Manager Mike Matheny remains hopeful it will pay off in the long run for Michael Wacha.

"We've got to do what we think is right," Matheny said after Wacha's shortest start of the season in an 8-5 loss to the Chicago Cubs on Tuesday night. "Sometimes you get immediate return and sometimes it's delayed, and you stick with what's right regardless."

Matheny added: "Michael wasn't far off from being really good."

Wacha (15-5) gave up six runs in four innings on 10 days' rest. Like Lance Lynn a day earlier, the 24-year-old right-hander got pushed back and then pummeled.

"I wouldn't put much into it," Wacha said. "I was still throwing bullpens in between and keeping the same kind of routine as if I was starting."

Lynn, held back three days by a sprained ankle he claimed felt fine, was spanked for six runs in 2 1-3 innings in a 9-0 loss on Monday.

Wacha had been 4-0 with a 1.70 ERA in six career September starts.

"Everything felt really good," Wacha said. "Just timing, really. Left a lot of balls up in the zone."

Starlin Castro and Anthony Rizzo homered and combined for seven RBIs as the Cubs won their fifth straight.

The Cardinals have the best record in the majors at 87-51, but have dropped five of six. Their lead over Pittsburgh in the NL Central slipped to 4 1-2 games. The Cubs are 6 1-2 back and are second in the NL wild card race behind the Pirates.

"Playing against those teams, they're always tough," said Jason Heyward, who walked twice. "We're going to beat up on each other, that's just part of it."

St. Louis was down 8-0 and had been outscored 24-1 over three games before pinch-hitter Randal Grichuk sparked a five-run seventh with a two-run homer estimated at 451 feet into Big Mac Land. Grichuk was activated from the disabled list strictly to pinch-run on Monday. He lobbied successfully to be considered at the plate after taking batting practice for the first time.

"I hadn't swung in three or 3 1-2 weeks, so yeah I was a little worried about it," Grichuk said. "I wanted to get out there and help the team win."

Grichuk got a second at-bat in the seventh, striking out with the bases loaded against Pedro Strop.

"It's very rare to do that," Grichuk said. "I kind of saw it getting closer and closer and I was pretty shocked I might get a second at-bat."

Rookie Stephen Piscotty had two hits and two RBIs for St. Louis.

"The seventh was good, it was fun to watch," Matheny said. "It was a real impressive job of our guys staying with it."

Jason Hammel (8-6) allowed three runs in six-plus innings for Chicago and Hector Rondon earned his 27th save in 31 chances.