SAN FRANCISCO -- Bryan Reynolds finally made it to San Francisco, and he delivered.
Reynolds hit a go-ahead single against his former team during a four-run rally in the ninth inning that sent the Pittsburgh Pirates to a 6-4 win over the Giants on Monday night.
Down 4-2, the Pirates used three pinch-hitters and came back against three Giants relievers in the ninth.
Kevin Newman hit a tying, two-run single with one out and Reynolds, a fellow rookie, followed with an RBI single off Jandel Gustave.
Reynolds also had a double and is batting .328. The Giants drafted him in the second round in 2016 before trading him to Pittsburgh after the 2018 season in a deal for Andrew McCutchen.
"It's pretty funny how that all worked out," Reynolds said. "It was fun to get out there and play. It's cold, but I have my sleeves."
José Osuna added a sacrifice fly in the ninth for insurance.
"Our team's been fun to watch and hard to watch sometimes because we can break your heart and we can make you jump up and down," Pirates manager Clint Hurdle said. "This isn't the first time we've done this."
Fernando Abad (0-2) gave up two hits and a walk while getting only one out.
The Giants were without All-Star closer Will Smith, shut down after experiencing some tightness throwing earlier in the day, manager Bruce Bochy said.
The Giants were 55-0 when leading after eight innings going into Monday.
"We took advantage of the men they put at the mound," Hurdle said. "From a professional standpoint, we handled our at bats, we made contact, we drove in runs and we won the game."
Richard Rodríguez (4-5) pitched a scoreless eighth inning. Felipe Vázquez worked the ninth for his 26th save in 29 chances.
Brandon Belt had three hits, including a two-run double for San Francisco. The Giants lost at home for the seventh time in eight games and fell to nine games below .500 at Oracle Park.
The announced attendance of 26,826 was the smallest at Oracle Park since April 12, 2010.
Belt's' two-out, two-run double in the fifth broke a 1-1 tie.
Giants starter Madison Bumgarner gave up two runs on six hits and two walks in seven innings.
"Too bad we couldn't hold on to give him a win," Bochy said. "You look at his body of work; he's been a savior. You have to those guys in charge. Guys who give you innings like that are invaluable — not just innings but quality innings."
Jacob Stallings homered for the Pirates.
The Giants took a 1-0 lead in the first when Evan Longoria singled in Mike Yastrzemski.
Giants catcher Buster Posey recorded his first career sacrifice bunt when he advanced Yastrzemski in the bottom of the first after 4,539 career at-bats.
Reynolds' 35th double tied Hall of Famer Paul "Big Poison" Waner (1926) for the Pirates' rookie record. . Giants center fielder Kevin Pillar took extra bases away from Osuna with a leaping catch against the wall with one out in the fourth. ... Newman hit safely in 13 of his last 14 games, batting .429 (24-for-56) three homers and 13 RBI over that stretch.
Pirates: OF Starling Marte was out of the lineup with a left wrist sprain he suffered making a diving catch in Sunday's game against St. Louis. Manager Clint Hurdle said his status is day-to-day.
Giants: RHP Reyes Moronta will undergo surgery on Tuesday to repair his injured labrum and capsule, manager Bruce Bochy said. The procedure will be performed by Dr. Neal ElAttrache in Los Angeles. . LHP Tony Watson underwent an MRI on Monday that showed a hairline fracture on his left wrist. Watson suffered the injury making a diving tag play in St. Louis on Sept. 5. He'll be reevaluated after wearing a splint for 10 days, Bochy said.
Pirates: RHP Mitch Keller (1-3, 8.18) left his last start on Sept. 4 in the second inning with a right wrist contusion after being struck by a line drive.
Giants: RHP Johnny Cueto (season debut) will make his first start since undergoing Tommy John reconstructive surgery. The two-time All-Star hasn't pitched in a major league game since July 28, 2018.
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