Bell's home run, his 25th of the season, came in the third inning off Baltimore starter Gabriel Ynoa and put the Pirates ahead 4-3. Bell also hit an RBI single in the first.
Ynoa (2-3) lasted just three innings and gave up four runs on five hits. He struck out three.
Gregory Polanco homered to lead off the second, his 11th this season and first since August 4.
Starling Marte singled and stole second in the fifth inning, giving him 20 steals for the fifth consecutive year, despite an 80-game suspension for violating baseball's performance-enhancing drug policy.
Chad Kuhl (8-11) went five-plus innings, allowing three runs on eight hits.
All the damage against Kuhl came in the second. Chance Cisco and Anthony Santander hit RBI doubles, sandwiching J.J. Hardy's run-scoring groundout.
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Pedro Alvarez started the rally with a single in his first game at PNC Park since leaving the Pirates. He played for Pittsburgh from 2010 to 2015.
Felipe Rivero pitched the ninth for his 20th save in 22 chances.
Orioles: RHP Jeremy Hellickson (sore back) and RHP Dylan Bundy (left hamstring strain) will both be shut down for the remainder of the season. ... SS Tim Beckham (right hamstring) missed his third consecutive game. ... CF Adam Jones (leg soreness) did not play for the second straight day.
Pirates: SS Jordy Mercer (knee) missed his third straight game.
Orioles: After an off day, Wade Miley (8-14, 5.52 ERA) will start the final series of the season Friday against Tampa Bay at Tropicana Field. Miley is 0-4 with a 9.92 ERA in September.
Pirates: Ivan Nova (12-11, 4.24) will start a four-game series in Washington on Thursday. Nova has lost four straight decisions and eight of his last nine dating to July 23.
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