SAN FRANCISCO -- Up to this point in the season, the Padres' bullpen has been one of their most consistent strengths. But in the past two games, it's played a role in their undoing.

The Padres suffered a walk-off loss at the hands of the Giants for the second straight game, falling 4-3 Tuesday night at Oracle Park. San Diego's top high-leverage arms were available -- unlike the night before -- but the end result was the same as San Francisco's batters again forged a late rally.

One stumble is an outlier. The Padres hope that two in a row are not the making of a trend.

"The last two games were definitely heartbreakers," said Nick Martinez, who gave up a game-tying homer to Joc Pederson in the eighth and was charged with the Giants' winning run in the ninth. "We've just got to keep chugging along. It's not always going to be rainbows and sunshine, so we've got to find a way to get the job done."

Entering the series, the Padres knew they had to slow down a hot-hitting Giants offense that was on its longest winning streak of the season. Michael Wacha's six innings of two-run ball on Monday did the trick until the bullpen buckled late in the game. 

The same was largely true for Seth Lugo, who made his return to the rotation Tuesday after missing just over a month with a right calf strain. He delivered five solid innings, allowing one run on three hits and a walk.

Lugo set the tone for a dominant evening by punching out five of the first six Giants batters he saw. He didn't record any additional strikeouts after the second inning, but his efficiency allowed him to complete five frames on 66 pitches, well within the boundary of his 65-70 pitch limit.

"For being out as long as he did and really not even having a rehab assignment," manager Bob Melvin said, "I thought he was about as good as he could be."

Lugo tinkered with his arsenal while he was on the injured list, and the results began to show Tuesday. He was pleased with the swing-and-miss his changeup generated, and his slider velocity was up a tick.

"A little better arm speed," Lugo said of his tweaks to his slider. "It kind of just comes out a little more like my fastball."

After Lugo exited the game with a 3-1 lead, the Giants began chipping away, all building up to another ninth-inning rally. Closer Josh Hader entered with one out and two on, issuing free passes to two of the three Giants he faced to walk in the winning run.

Lugo, who spent the vast majority of his career pitching in relief before converting to a starting role this season, understands better than anyone the streaky nature of life in the 'pen.

"Easier said than done, but you've got to flush it," he said. "Once we walk out of here tonight, we've got to get our rest and come back tomorrow, and play like we know how to play and forget like today ever happened."

Two disappointing games were not enough to tank the numbers for a San Diego bullpen that has otherwise been excellent in 2023. Padres relievers have combined for a 3.37 ERA, the lowest mark in the National League and third-best in the Majors.

"We could have probably added on in some spots, and I think that ended up probably being the difference," Melvin said. "We got nicked up for one run in the seventh, eighth and ninth. … A lot of times, what happens earlier in the game kind of dictates where it goes sometimes."

As in any game, the onus for the loss didn't fall entirely in one area. Ha-Seong Kim was picked off at third base in the fourth, ending a potential rally before it started, and San Diego's funk at the plate with runners in scoring position persisted with a 2-for-10 showing. 

"It blows the wind out of us, a game like this," said Fernando Tatis Jr., who hit his team-leading 15th homer to lead off the fifth inning. "But we've got to keep battling and keep showing like we have been. This bullpen has been lights-out all year, so we've just got to pick our boys up."