CHICAGO — No matter the momentum built over the past few days, any winning streak longer than three games continues to be a hump the Giants cannot get over.

They looked well on their way, or at least well-positioned, to win their fourth straight for the first time all season Saturday afternoon after Rafael Devers put them ahead with his eighth homer while Landen Roupp cruised through the first five frames in a strong bounce-back effort.

The Giants’ Rafael Devers rounds the bases after hitting a home run against the Cubs on Saturday. AP Photo/Paul Beaty

It all fell apart thanks to a familiar culprit.

Their bullpen.

Roupp allowed Pete Crow-Armstrong to tie the score on a mammoth home run to lead off the sixth, and after escaping two bases-loaded jams in the sixth and seventh, San Francisco’s relievers couldn’t hold on any longer.

One out from securing a 2-1 win that would have been their fourth in a row, Crow-Armstrong did it again. He demolished the first pitch he saw from Keaton Winn and sent it toward the scoreboard in right field, sending the game to extra innings.

The Cubs sent the Giants onto the streets of Wrigleyville 3-2 losers with their MLB-leading eighth walk-off win of the season when Victor Bericoto booted a line-drive single by Michael Busch in the 10th that allowed Moises Ballesteros to score from second.

Ballesteros was initially held up at third until Bericoto failed to field the ball cleanly.

Bericoto entered the game as a pinch-hitter for Winn, the pitcher, who was due up in the order in the top of the 10th because manager Tony Vitello pinch-ran for designated hitter Bryce Eldridge with Jonah Cox and opted to keep Cox in the game for defense over Casey Schmitt, who was in left.

It resulted in the Giants playing without their slugging top prospect or their team leader in home runs the rest of the game, with the inexperienced Bericoto in right.

“I mean, we got where we wanted,” Vitello said. “Their best player did what he did and from that point on, you’re chasing your tail a little bit on the road. … Schmitty, I don’t think can be labeled just an infielder anymore, he’s spent plenty of time out there. But obviously with the lead, we want our best defense out there in the outfield.”

Winn was attempting to record his fifth out after entering the game in the eighth, a similar task he executed to secure his first career save in the Giants’ 1-0 win against the Brewers earlier this trip.

“Same deal tomorrow with Keaton — still have faith in him,” Vitello said. “What he did in Milwaukee was tremendous.”

After banging out 19 hits and 18 runs a day earlier, the Giants were held to five hits by Ben Brown and the Cubs’ bullpen, with their only offense until the ninth coming on Devers’ solo shot.

Two of their hits came from Jung Hoo Lee, who extended his hitting streak to a career-best 14 games. He and Eldridge ignited a rally against Cubs closer Daniel Palencia to give them a brief 2-1 lead in the ninth. But they were unable to advance, let alone score, the automatic runner on second base in the top of the 10th.

“I don’t think you’re ever OK with a loss, but … we’re playing good ball,” Vitello said. “We played good today. They absolutely battled their [rear ends] off.”

The Cubs’ Pete Crow-Armstrong watches one of his two home runs Saturday against the Giants. AP Photo/Paul Beaty

What it means

The Giants didn’t invest in their bullpen this offseason, and Saturday’s loss was just the latest instance of it coming back to bite them.

Without a clear closer, Vitello burned through Caleb Kilian and Erik Miller before handing a tied game over to Winn, who retook the mound in the ninth holding a 2-1 lead.

Since ending April with the second-best bullpen ERA in the majors, the Giants’ patchwork bullpen has regressed to the league’s fourth-worst group, with a 5.22 ERA.

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Who’s hot

Roupp looked no worse for the wear after dealing with back tightness in his last start.

After laboring through 96 pitches to complete four innings while surrendering eight runs in his last start, Roupp’s velocity was back to normal, and he cruised through 5 ⅔ frames.

“I felt good today,” Roupp said. “I thought today was a step in the right direction for me.”

The only damage the Cubs did against Roupp came on Crow-Armstrong’s first homer that tied the score at 1 to begin his final inning, but after putting the next batter on with his third walk, Roupp responded by getting Busch and Alex Bregman to swing through off-speed pitches at the knees for the next two outs.

“Overall, I think I made a lot of good pitches,” Roupp said. “Really one mistake all day was the fastball to PCA.”

The Giants’ Jung Hoo Lee and his teammates saw their three-game winning streak snapped Saturday. Matt Marton-Imagn Images

Who’s not

Eric Haase lost a low-leverage ABS challenge, leaving the Giants with just one for the rest of the game, when he tried to overturn a ball below the strike zone in the first inning with nobody on and two outs.

It wasn’t the first time this trip the Giants chose a poor time to deploy their challenges. They were forced to protect a 1-0 ninth-inning lead against the Brewers without a challenge remaining Wednesday when Drew Gilbert lost their last one on an upheld strike in the top half of the inning. 

On the season, the Giants have been one of the majors’ least effective teams using the ABS system — one of six teams to lose more than they win (48%) with 16.5 fewer overturns than expected, according to Statcast.

Up next

The Giants and Cubs are scheduled to square off at 5:30 p.m. PT on NBC’s nationally televised “Sunday Night Baseball.”

With an expected 4 a.m. arrival back in San Francisco and a date with the Nationals later that evening, the Giants sent Logan Webb, their scheduled starter, home ahead of the team.

“The travel,” Vitello said, “will be a little bit of a kick in the groin.”