By Bruce Levine–

CHICAGO (CBS) — Who’s the ace of the Cubs’ pitching staff?

That’s been an ongoing conversation over the past three seasons. In 2015, it was all about Cy Young-winning right-hander Jake Arrieta. In 2016, Arrieta was good and left-hander Jon Lester and right-hander Kyle Hendricks were even better, with those two combing for 53 wins.

The Cubs’ rotation has been less predictable this season, in part because of injuries. Hendricks missed much of June and July with a finger ailment, and Lester has been out since mid-August with shoulder fatigue. As those injuries have taken a toll, the one constant since the All-Star break has been Arrieta, who after firing six shutout innings in a 4-1 win against the Pirates on Tuesday at Wrigley Field is now 6-1 with a 1.59 ERA in nine starts in the second half.

Arrieta didn’t have his best command but was still dominant in scattering two hits and two walks while striking out four.

“That was kind of the key for me tonight,” Arrieta said. “I did not have great stuff tonight. When I talked to Joe (Maddon), I told him tonight that was just competing. I tried to mix up things and keep them off balance. They fouled off a lot of good pitches. I was able to make a couple of quality pitches when I needed to. Tonight I was able to make do with what I had and get the job done.”

Arrieta threw 97 pitches through six innings, and that elevated count prevented him from going as deep into the game as he would’ve liked. A lack of command on his slider was part of the reason Arrieta ran his pitch count up early, but the Cubs were thrilled with his effort that marked Arrieta’s 14th win of the season.

With his free agency looming in November, Arrieta is pitching near his top form. On Tuesday, he improved to 68-29 in his four-plus years with the Cubs. His 54 wins since the start of 2015 are the most of anyone in baseball.

“He did not have his best everything, but he pitched,” Maddon said. “He competed. A lot of foul balls. He wasn’t missing bats. He kept extending at-bats. I give him credit, he didn’t have his usual command. When you compete like that, you deserve the win.”

Keeping Arrieta and the other pitchers fresh with pitch counts near 100 per outing has been part of the Cubs’ big-picture vision this season, as they want to keep the rotation from burning out after deep playoff runs in 2015 and 2016. That philosophy appears to be working well with 31 games left in the regular season.

The Cubs now lead the NL Central by 3.5 games over the Brewers.

“I thought he was extended at that point,” Maddon said of taking Arrieta out after six innings. “A couple of years ago, I might have kept him in. You have to read it in the dugout. I thought that was pretty much his Waterloo tonight. Everybody is different, but that is what I saw. This is not a hundred-pitch exercise. You must read it every night. I do agree that we have done a good of not overextending our guys to this point.”

Bruce Levine covers the Cubs and White Sox for 670 The Score and Follow him on Twitter @MLBBruceLevine.

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