Brian Bogusevic went 3 for 4 with his fifth homer of the season for Chicago. Dioneer Navarro added two hits as the Cubs ended Pittsburgh's four-game winning streak.
Carlos Villanueva (6-8) picked up the win in relief. Kevin Gregg worked the ninth for his 32nd save.
Pedro Alvarez, Russell Martin and Garrett Jones hit consecutive solo home runs in the fourth for Pittsburgh. Andrew McCutchen went 2 for 4, but the Pirates lost for just the fourth time in 65 games when leading after six innings this season after Grilli (0-2) faltered.
Grilli, an All-Star in July after racking up 29 saves in the first half of the season, is still working his way back from a strained forearm that sidelined him for more than six weeks. Pittsburgh manager Clint Hurdle moved Grilli into a middle relief role when he was activated off the 15-day disabled list earlier this month.
Pitching in his first pressure situation since his return, Grilli entered with the Pirates up a run in the seventh. He nearly got out of the inning clean, but Luis Valbuena walked on a borderline 3-2 pitch. Rizzo followed by turning on an 83 mph slider and sending it clear over the stands in right field for his first home run since Aug. 30.
Chicago's bullpen made it stand up, silencing Pittsburgh over the final three innings after the Pirates erased an early 3-0 deficit against starter Jake Arrieta.
Arrieta breezed through the first three innings and was on his way to doing it in the fourth when Pittsburgh broke out. Alvarez hit a fly ball to the wall in right-center with two outs that neither center fielder Ryan Sweeney nor right fielder Nate Schierholtz could corral. The 235-pound Alvarez chugged all the way around the bases for his 33rd -- and by far most wearying -- home run of the season.
Alvarez was still catching his breath when Martin followed with a shot 10 rows deep into the stands in left to bring the Pirates within one. Jones tied it seconds later by sending a laser into the seats in center. It marked the first back-to-back-to-back home runs by the Pirates since Jason Kendall, Brian Giles and Reggie Sanders did it on Aug. 20, 2003, in St. Louis.
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Pittsburgh eventually took the lead in the sixth when reliever Brooks Raley mishandled a lob from Rizzo at first base, allowing McCutchen to race all the way home from second.
The Pirates have risen to the top of the NL Central behind the strength of a bullpen led by the irrepressible Grilli. His velocity, however, has dipped since his comeback and Rizzo took advantage.
Pittsburgh starter Charlie Morton struggled keeping the ball down while trying to bounce back from his worst start since returning from reconstructive surgery on his right elbow in June. Morton allowed three runs in five innings, including a two-run homer by Bogusevic in the fourth and saw a handful of balls caught at the warning track on a night a stiff breeze from the north kept the outfielders busy.
NOTES: The Pirates will consult with specialist Dr. James Andrews before figuring out the next step for LHP Wandy Rodriguez, who has been out since June with left forearm tightness. Rodriguez threw 67 pitches in a simulated game on Thursday ... The Cubs named infielder Javier Baez as the club's minor league Player of the Year and RHP Kyle Hendricks as its minor league Pitcher of the Year. The 20-year-old Baez hit .282 with 37 home runs and 111 RBIs in 130 games between Class-A Daytona and Double-A Tennessee. Hendricks went 13-4 with a 2.00 ERA and one shutout in 27 starts between Tennessee and Triple-A Iowa ... The series continues on Saturday when Pittsburgh's Gerrit Cole (7-7, 3.48 ERA) faces Chicago's Scott Baker (0-0, 0.00). Baker is making his second start since reconstructive elbow surgery.
Press; By WILL GRAVES]
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