MIAMI -- The Miami Marlins had hit into five double plays.

They had made three errors.

They had been outhit 14-5 entering the ninth inning, and another loss during what has been a dismal first-half of the season seemed imminent.

But Justin Bour turned all that around with one left-handed swing.

Bour hit a walk-off three-run homer with no outs in the bottom of the ninth to lead the Marlins to a 6-5 win over the San Francisco Giants on Wednesday night at Marlins Park.

Bour's teammates splashed him with water bottles and Gatorade as he came across home plate.

"My jersey's soaked, and it might be ruined," Bour said of the celebration.

Asked for his favorite part of the jubilation he shared with teammates, Bour said, "Probably (second baseman) Dee (Gordon) hanging on the back of me -- that was pretty fun."

The Marlins (33-46) gave up two unearned runs. Their five double plays tied a Giants franchise record for a nine-inning gmae.

San Francisco (42-37) got a tiebreaking home run by shortstop Brandon Crawford in the sixth inning. It was his 11th homer of the season, a career high.

But the big hit was wiped out when Bour pulled his shot to right field off Giants right-handed reliever Santiago Casilla (4-2).

"Our closer (Casilla) was off (his game) tonight," Giants manager Bruce Bochy said. "That was the difference in the game."

Giants catcher Andrew Susac called for a curveball on the 1-0 pitch that became Bour's game-winner. But Casilla shook off the sign and went to his favorite pitch, the sinker.

"I'm always confident when he throws the sinker," Susac said. "It's a pretty good pitch. That one happened to run back over the plate."

It was Bour's first-career walk-off home run and his eighth homer of the season. All eight homers are against right-handers.

The last Marlins player to hit a walk-off homer was right fielder Giancarlo Stanton, who beat Seattle with a grand slam on April 18, 2014.

Bour started this season on a roll, hitting .369 with five homers in 25 games through April and May. But in 21 games in June, he came crashing down to earth, hitting just .138 with two homers.

"When we took him in the Rule 5 Draft, we knew he could hit," Marlins manager Dan Jennings said. "He really swung the bat well when he first got here. Then he had a little spell where his timing was off.

"But over the past three or four games, his timing is back. He's not just a power guy – he's a hitter. He can spray the ball around."

For the season, Bour is hitting .265 vs. right-handers and .154 vs. lefties.

Marlins reliever Steve Cishek (2-5) picked up the win, pitching a scoreless ninth.

San Francisco took a 1-0 lead in the third. Right fielder Justin Maxwell, making his first start of the series, hit a leadoff single and came around to score with two outs when a low throw by shortstop Adeiny Hechavarria got past Bour at first base.

It was the second straight game when the Giants scored on a play in which Bour did not scoop a low throw. On Tuesday, the error went to third baseman Derek Dietrich. But this time Bour was charged with an error.

Miami took a 3-1 lead in the bottom of the third. Right fielder Cole Gillespie hit a leadoff double and scored when starting pitcher Dan Haren faked a bunt and drilled a single to right, getting it past a drawn-in infield.

Gordon then grounded a triple just inside the first-base bag, driving in Haren. Gordon capped the rally when he scored on a double-play grounder by Hechavarria.

The Giants cut their deficit to 3-2 when left fielder Gregor Blanco hit an RBI single in the fourth.

San Francisco took a 4-3 lead in the sixth. Third baseman Chris Duffy hit a leadoff double and came around to score on first baseman Brandon Belt’s sacrifice fly. Crawford followed by pulling his solo home run to right.

NOTES: Giants C Buster Posey went 1-for-2, leaving the game after gettting hit by a foul pitch. Posey said he got "his bell rung" but felt good. He will go through tests for a possible concusssion. ... Marlins RHP Jose Fernandez will make his long-awaited return from Tommy John surgery on Thursday against the Giants. He hasn't pitched since May 9, 2014. ... The Giants on Thursday will start RHP Matt Cain (elbow and ankle surgery), who has not pitched since July 9, 2014. The Giants are expected to place RHP Tim Lincecum (forearm) on the DL to open a roster spot for Cain. … RF Cole Gillespie made his first start as a Marlins player. ... Marlins RHP Henderson Alvarez (shoulder inflammation) threw a 30-pitch bullpen session on Tuesday and could start a rehab assignment after the All-Star break. ... Lawson Crouse, the Florida Panthers' 2015 first-round draft pick, threw out the first pitch. Last week, before the draft, Crouse was one of six top prospects who took batting practice at Marlins Park and was the only one who hit a homer.