SAN FRANCISCO -- Madison Bumgarner couldn’t savor the 19th home run of his career without also lamenting one of his missteps on the mound.

Asked to describe the pitch he crushed out to left field in the third inning, Bumgarner said, “Fastball down the middle. Same pitch I threw to [Ian] Desmond.”

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Bumgarner’s blast, and the three home runs he allowed, felt like a distant memory by the time the Giants fell to the Rockies, 8-5, in 16 innings following a five-hour, 31-minute marathon that stretched into early Wednesday morning at Oracle Park.

Buster Posey and Bumgarner homered to give the Giants an early 3-1 lead, but the Rockies came back to tie the game on Desmond’s two-run shot in the fourth. The National League West rivals traded runs in the fifth before Garrett Hampson crushed his second home run of the night to put the Rockies back ahead, 5-4, in the eighth. Evan Longoria countered with his 20th home run of the season, a game-tying solo shot in the bottom half of the inning.

A prolonged stalemate ensued, with both club’s bullpens matching each other with seven scoreless innings before the Rockies finally broke through in the top of the 16th on Charlie Blackmon’s three-run, go-ahead home run off Dereck Rodríguez. A combined 25 pitchers were used in the game, setting a Major League record.

“The long ball got us,” manager Bruce Bochy said. “Bum didn’t give up a lot of hits, but the ones he did give up unfortunately left the ballpark. Of course, the last one there was the one that did us in. But you know what, the ‘pen did a great job. We went, what, seven, eight innings without scoring a run. We just couldn’t find a way to put one across the board there, unfortunately.”

With only five games left to play, the loss guaranteed that the Giants (75-82) will finish with a losing record for the third consecutive season.

Bumgarner yielded four runs -- all on homers by Hampson, Desmond and Trevor Story -- over seven innings and came away with a no-decision in his penultimate start of the season, and perhaps of his Giants career. He is scheduled to start Bochy’s final game on Sunday against the Dodgers before becoming a free agent in the offseason.

Bumgarner said he has not yet begun to grapple with the potential end of his Giants tenure, preferring to save those reflections for the end of the season.

“I haven’t really thought about it much,” Bumgarner said. “I just spent the last few days getting ready for this start and [I will] do the same for the next few days. After the season is over, maybe I’ll look back on this last little bit. But right now, I’m just getting ready for the next start.”

Bumgarner, who has recorded a 3.90 ERA over 207 2/3 innings this season, figures to be one of the top free-agent starters available this winter, leaving his future in San Francisco a bit murky.

Re-signing Bumgarner would return a veteran workhorse to the top of the Giants’ rotation and add much-needed depth alongside Johnny Cueto and Jeff Samardzija, but it’s unclear if first-year president of baseball operations Farhan Zaidi would be willing to offer the type of long-term deal the 30-year-old left-hander will likely be seeking this winter.

Bumgarner’s pronounced home-road splits could bolster the Giants’ efforts to hold on to their longtime ace. While Bumgarner posted a 5.29 ERA over 15 starts on the road this year, he remains elite at Oracle Park, where he’s logged a 2.93 ERA over 19 starts.

He allowed only six hits to the Rockies on Tuesday, though three of them left the ballpark. Bumgarner has surrendered a career-high 30 home runs this season, though he believes the spike can be partly attributed to the way the balls have been carrying this year.

“You’ve basically just got to touch it, if you put it in the air,” Bumgarner said. “It’s what it’s been. We know that. It’s not like it’s catching anybody by surprise. You’ve just got to do what you can to make pitches and limit that. But it’s part of the game.”