PITTSBURGH (AP) Kevin Newman felt the entire crowd on his side when he stepped to the plate in the ninth inning of a tie game.
Tucker worked a walk off Brandon Kintzler (2-2), and Newman followed with a single to center field on a full count for his third game-ending hit of the season.
''It's funny, but I was up there as the crowd was getting really wild and I felt kind of like everybody was on my side in the crowd,'' Newman said. ''I know there were a good amount of Cubs' fans there, but it was kind of like it was everybody and me against the Cubs.''
Kintzler walked three batters in 1/3 of an inning, including an intentional walk to Josh Bell with two outs and the Cubs leading 2-1. Erik Gonzalez entered as a pinch runner for Bell and scored on Newman's single.
Kintzler was activated from the injured list prior to the game after missing 10 days with right pectoral inflammation. The Cubs are without closer Craig Kimbrel, who is on the injured list with right knee inflammation.
''I didn't anticipate that part. None of us did,'' Cubs manager Joe Maddon said of the walks. ''He's been so good for all year. It's unfortunate. Kintzler's the right guy right there. It didn't play out.''
''They put up some good at-bats,'' Kintzler said. ''I just got tired, I think, and the legs got a little wobbly.''
Tucker's walk on a seven-pitch plate appearance kept the Pirates' rally alive. A rookie shortstop like Newman, Tucker was recalled from Triple-A Indianapolis prior to the game.
''I calmed down and felt really good up there,'' Tucker said. ''I felt like I had done it before, even though I hadn't. That'll probably be the coolest walk I'll ever have in my career.''
The Cubs fell to 23-39 on the road. They have also lost 17 of their last 25 games away from Wrigley Field. The loss left Chicago a game behind the NL Central-leading St. Louis.
The Pirates won for the third time in four games after losing 24 of their previous 28.
Tony Kemp's two-run triple in the eighth inning off closer Felipe Vazquez gave the Cubs a 2-1 lead.
Joe Musgrove carried a shutout into the eighth before giving up consecutive singles to Jonathan Lucroy and pinch-hitter Ian Happ with one out. Musgrove was charged with two runs in 7 1/3 innings, giving up four hits and no walks. He matched his career high with nine strikeouts.
Musgrove retired his first 11 batters before Kris Bryant singled with two outs in the fourth inning. He also set down 10 straight hitters before the hits in the eighth inning.
''It was probably the best I felt all year,'' Musgrove said.
Keone Kela (2-0) pitched a scoreless ninth for the win.
Cubs starter Kyle Hendricks allowed only one run and three hits in seven innings with one strikeout and one walk.
The Pirates' Colin Moran had an RBI single in the fourth.
Cubs: In addition to Kintzler being activated, INF Addison Russell was recalled from Triple-A Iowa and CF Albert Almora Jr. and RHP James Norwood were optioned there.
GM Jed Hoyer said Almora is expected to be recalled Sept. 1, when the roster limit expands to 40 from 25. Almora made 75 starts in center field and hit .232 with 12 home runs and 32 RBIs in 114 games.
Pirates: RHP Geoff Hartlieb was optioned to Indianapolis to clear a roster spot for Tucker. The Pirates wanted an extra position player because INF/OF Jose Osuna is two games into the five-game suspension he received from Major League Baseball for his part in a fight at Cincinnati on July 30.
Tucker made his major-league debut April 20.
Cubs: SS Javier Baez (illness) and CF Jason Heyward (left knee inflammation) returned after being held of the lineup in Thursday night's loss at Philadelphia. . INF Daniel Descalso (sprained left ankle) will begin a rehab assignment with Iowa on Saturday.
Pirates: C Jason Stallings (migraine) started after being scratched from Wednesday's loss at the Los Angeles Angels.
Cubs LHP Jon Lester (9-8, 4.48 ERA) faces LHP Steven Brault (3-1, 4.33) on Saturday. Lester is winless in his last five starts, going 0-2 with a 7.00. Brault has had two no-decisions, allowing six runs in 10 innings, since missing a month with a strained shoulder.
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