SAN FRANCISCO -- Forty-eight minutes after midnight on Saturday, rookie left-hander Travis Bergen found himself standing near the on-deck circle bracing for his first at-bat since 2012, when he was a high school player in Georgia.

It was the bottom of the 18th inning, and Bergen was the last reliever standing for the Giants.

“I was scared to death,” Bergen said. “I was trying to decide if I was going to swing at the first pitch or not. I think I flipped back and forth probably like 50 times in what felt like the three hours I was standing out there.”

But Bergen didn’t end up making it to the batter’s box. A five hour and 35-minute staredown between the Giants and the Rockies finally came to an end after Erik Kratz grounded into a fielder’s choice that allowed Brandon Belt to score the winning run and propel San Francisco to a 3-2 victory at Oracle Park.

The 18 innings matched the longest game in the ballpark’s history, equaling the length of the Giants’ 1-0 loss to the D-backs on May 29, 2001.

“You don’t prepare to play 18 innings, but it’s just like anything else, you take it one pitch at a time,” said the 38-year-old Kratz, who caught the whole game. “I got a second wind in the 17th inning, I think.”

Belt, whose 18th-inning home run lifted the Giants to victory over the Nationals in Game 2 of the 2014 National League Division Series, ignited the comeback by driving a 3-2 fastball from DJ Johnson off the right-center-field wall for a leadoff double.

“I’m the best 18th-inning hitter that ever lived,” Belt joked afterward. “I’m 2-for-2 in the 18th inning.”

Intentional walks to Brandon Crawford and Gerardo Parra loaded the bases for Kratz, who entered Friday just 2-for-13 in his first six games with the Giants.

Kratz fell behind, 0-2, before bouncing a grounder to the right side that was fielded by center fielder Ian Desmond, who was playing near second as part of the Rockies’ five-man infield. Desmond’s throw beat Belt to the plate, but catcher Chris Iannetta’s foot was in front of the plate, and Belt was called safe to secure the Giants’ first walk-off win of the season.

“I tried to play it like a first baseman, and my foot didn’t stay on the base,” Iannetta said. “I felt like I’d never played baseball before. I don’t think I’ll be sleeping much after this one.”

Kratz became the first player to catch at least 18 innings and deliver the game-winning RBI in the same game since the Angels' Bob Boone on April 13, 1982, against the Mariners.

“He’s 38 years old, and he caught that whole game,” manager Bruce Bochy said. “He battled, and he put the ball in play. That’s what you want. Things can happen when you do that. We had to stay away from a strikeout. They almost made a great play on it, but it’s nice to end that game, I’m not going to lie.”

The Giants struggled to put much pressure on the Rockies’ pitchers between the seventh and 17th innings, but a stellar effort from their bullpen kept them in the game and gave them a chance to rally. After left-hander Drew Pomeranz departed after allowing two runs over five innings, eight Giants relievers combined to fire 13 scoreless innings, allowing only seven hits and striking out 19.

The Rockies threatened in the eighth after Trevor Story singled to load the bases with one out, but left-hander Tony Watson managed to evade damage by inducing a lineout from Desmond and striking out Josh Fuentes to end the inning, keeping the 2-2 tie intact. Mark Melancon was also tested over his two innings of work, but he dodged trouble and left the go-ahead run stranded at third in the 11th.

“What a job that bullpen did,” Bochy said. “All of them. Just a really good effort. They had some chances, and we got out of it. We had a pretty good window where we couldn’t get a man on second base, so that’s a great win. We used everybody, and we stretched some guys out to where they hadn’t been very often. They really pitched their hearts out and won that game for us.”