MILWAUKEE (AP) -- Anthony Rizzo hit a three-run double in the seventh inning and the Chicago Cubs rallied from a four-run deficit to beat the Milwaukee Brewers 6-5 on Sunday.
The Cubs broke through against the Brewers bullpen after struggling with runners in scoring position against starter Junior Guerra.
That changed after Will Smith took over for Guerra with one out in the seventh.
Tommy La Stella went 3 for 3 for Chicago. He had an RBI double before Smith (1-3) walked Kris Bryant to load the bases for Rizzo. He hit a 2-2 slider down in the zone into right-center to clear the bases and give Chicago a 5-4 lead.
The rally made a winner of reliever Joe Nathan (1-0) in his first game in the majors since April 2015. He was activated off the 60-day disabled list earlier Sunday, completing his comeback from Tommy John surgery.
But Cubs pitchers labored for much of the afternoon, with starter Jon Lester struggling through four innings, allowing four hits and walking five.
Nathan gave up a leadoff triple to Jonathan Villar in the sixth and a walk before striking out 3-4-5 hitters Ryan Braun, Jonathan Lucroy and Chris Carter.
Ben Zobrist's RBI single scored Rizzo in the seventh and gave the Cubs a needed insurance run after closer Hector Rondon gave up a homer to Kirk Nieuwenhuis with two outs in the ninth to draw Milwaukee within a run.
Rondon struck out Jake Elmore looking for his 18th save.
Smith's struggles overshadowed another solid start by 31-year-old rookie Guerra, who allowed five hits and one unearned run over 6 1-3 innings.
The Brewers built their 4-0 lead, stealing six bases in a game for the first time since May 13, 2013. Braun and Villar each had two steals off Lester by the bottom of the second.
Cubs: Nathan, a six-time All-Star, signed with the Cubs as a free agent in May and went on the DL. "It feels like opening day," Nathan said before the game. Right-hander Adam Warren was optioned to Triple-A Iowa in a corresponding move. ... SS Addison Russell left the game before the bottom of the fourth with a left heel contusion.
Brewers: Will Middlebrooks left the game before the top of the fourth a lower right leg strain. The third baseman popped out in the bottom of the third.
Cubs: Jake Arrieta (12-4) takes the mound when Chicago travels to the South Side for an interleague series against the crosstown-rival White Sox. The right-hander is 3-1 with a 3.82 ERA in six starts against the White Sox.
Brewers: Chase Anderson (4-10) opens a four-game series against his former club, the Arizona Diamondbacks. The righty has struggled over his past six outings, going 0-4 with a 9.13 ERA.