Playing in his fourth major-league game, Polanco broke a tie in the 13th inning with his first homer, helping Pittsburgh to an 8-6 victory over the Miami Marlins after the Pirates had a ninth-inning meltdown.
Polanco went 5 for 7, scored three times and made a run-saving catch in right field.
"That could have been a coming-out party for him," manager Clint Hurdle said. "Very exciting to watch. I hope we get to watch for a long time."
Clint Barmes singled off Mike Dunn (5-4) to start the 13th and advanced on a sacrifice. Polanco homered on a hanging 2-2 slider and smacked his hands as he circled the bases, mindful his mother was in the stands watching him for the first time since he played winter league in his native Dominican Republic.
"For sure this is my best game ever -- the first time she's here watching me play," Polanco said. "I was excited and a little emotional. She's so proud of me, and I know she's feeling excited right now."
Jeanmar Gomez (1-2) pitched four scoreless innings after the Pirates blew a 6-2 lead in the ninth when three relievers combined to issue six walks. The Pirates' Jeff Locke pitched a career-high eight innings, and the bullpen's wildness cost him his first victory since Sept. 12.
Miami trailed 6-5 and had runners at first and third with two out in the ninth when Hurdle ordered NL home run and RBI leader Giancarlo Stanton intentionally walked. The strategy backfired when Casey McGehee fell behind 0-2, and then walked against Mark Melancon to tie the game.
Melancon struck out Marcell Ozuna to send the game to the 10th.
"You rip off the rearview mirror and keep playing," Hurdle said.
The Marlins stranded three in the ninth and two in the 12th.
"The game was there for the taking at the end," McGehee said. "It was unfortunate we couldn't quite finish it off."
The Pirates have won seven consecutive series openers, and on Saturday they have a chance to reach .500 for the first time since mid-April.
Miami's Nathan Eovaldi pitched as though he was more worried about his wife's delivery than his own, which was understandable. Their first child is due, which left Eovaldi's status in doubt until game time, and he allowed 10 hits and six runs in 4 2/3 innings.
Stanton hit his 18th home run. Rafael Furcal, making his season debut after being sidelined by injuries since 2012, turned two double plays at second base but went 0 for 6.
Locke, making his second start since right-hander Gerrit Cole went on the disabled list, allowed two runs, seven hits and no walks. The left-hander said he was encouraged by his performance.
"It's huge," he said. "Anytime you give this team a chance to win, it makes you feel good. That's what I've always tried to do through the struggles and the successes. It builds a lot of confidence moving forward."
Locke made the NL All-Star team last year but pitched poorly the second half of the season and has spent most of this season in Triple-A.
Marlins LF Christian Yelich left the game in the second inning with a strained lower back. His status is day to day. ... 2B Michael Martinez made his first start with the Pirates and went 0 for 3. ... Pirates OF Josh Harrison (ankle) was held out of the lineup. ... Former Pirate Garrett Jones pinch-hit in the ninth for Miami and struck out. ... The Pirates' Russell Martin was safe at second when the Marlins botched a rundown in the fourth, but the call was reversed following a replay review and he was ruled out. ... Martin made his 1,000th career start at catcher, which ranks fifth among active players. ... RHP Stolmy Pimentel and RHP Vance Worley are candidates to start Sunday for the Pirates in place of LHP Francisco Liriano (left oblique strain). ... LHP Randy Wolf (1-2, 4.15 ERA) is scheduled to start Saturday for Miami against RHP Charlie Morton (3-7, 3.14 ERA).