MILWAUKEE -- The Chicago Cubs aren’t exactly rolling, but the series wins keep piling up and they remain securely on their first-place perch.

That happy tale looked grim for much of Sunday’s 6-5 victory in Milwaukee. Jon Lester suffered through his third lackluster outing in his past four starts. The offense managed just one unearned run through six innings and at that point, the hitters had managed just three runs altogether in its past 22 innings against the Brewers.

Then two key sequences changed everything.

In the bottom of the sixth, the Cubs trailed 4-1 and veteran Joe Nathan came on to pitch to make his Cubs debut. He had not pitched in a big-league game in more than 15 months. At first, the rust showed. He gave up a sharp triple to Jonathan Villar, and walked Hernan Perez.

“Too many nerves, but that’s a good thing for me,” Nathan said. “When the nerves go away, it’s probably time to hang it up. The nerves were full tilt. It felt like Opening Day to me today.”

Up stepped dangerous Ryan Braun and Nathan fell behind 2-0, which sent pitching coach Chris Bosio trotting out to the mound for a chat. The pep talk worked, as Nathan morphed into the guy with 377 career saves, striking out Braun, Jonathan Lucroy and Chris Carter in succession.

“That was a [difficult] moment for him,” Cubs manager Joe Maddon said. “Double, second and third, and here comes Braun, Lucroy and Carter. He made good pitches to every one of them.”

That in itself is a nice little anecdote but Anthony Rizzo turned it into a major plot point in the top of the seventh. With one out and nothing brewing for Chicago, Milwaukee starter Junior Guerra was replaced by lefty Will Smith. Five batters later, Smith exited without retiring a batter and the Cubs in the lead.

Rizzo hammered the big blow, a drive into the right-center gap to clear the bases that put Cubs in front 5-4. Rizzo pumped his fist as he pulled into second, giving expression to a game-turning moment, though it's one he's familiar with. According to research by ESPN Stats & Info, it was Rizzo's 17th career go-ahead hit in the seventh inning or later of a game.

“It was a complete victory,” Maddon said. “Rizz had a couple of tough at-bats and gets a big hit. [Players] up and down the lineup continuing to work good at-bats. Great, great team win.”

Chicago held on from there, giving Nathan his first win since Sept. 23, 2014, when he was with Detroit.

“Put myself in a hole right out of the chute, but I think that [Bosio] was able to come out and kind of slow it down a little bit for me,” Nathan said.

It was a weird start for Lester. He, along with his regular catcher, David Ross, allowed five stolen bases in the first two innings, matching a career-high for Lester. Even in his scoreless second, Lester needed five outs to escape the inning after two runners reached on errant strikeout pitches.

The ugly line for Lester: four innings, four runs, five walks, five steals allowed, a wild pitch and seven strikeouts. Yet it could have been much worse.

“Usually a lot cleaner than that,” Lester said. “Wasn’t too clean. Kind of minimized the damage a little bit, and just tried to move on. I was able to do that, with better results in that second inning. Kind of a weird game, as it was.”

The Cubs have now won all three of their series since the All-Star break ended, taking two of three each time.

Cubs shortstop Addison Russell departed the long, stifling day early. He was pulled from the game after flying out to end the fourth. Russell hit his heel on a backswing during his first at-bat in Saturday’s game. In what is being termed a left-heel contusion, Russell felt some discomfort during his appearance and was removed mostly as a precautionary measure.

The injury isn’t believe to be serious, though Maddon says he may give Russell another day’s rest when the Cubs open their crosstown series against the Chicago White Sox on Monday.

That series promises to be a wild one, with trade rumors circulating around both teams and with the fallout of White Sox ace Chris Sale's suspension. Even with the Chicago teams seemingly headed in opposite directions, the Cubs will have to recalibrate to prepare for is always a raucous atmosphere.