Both pitchers will try for a third straight win in Wednesday's decisive series finale between the NL West foes.
San Diego (36-35) had a seven-game winning streak snapped with a 5-4 loss Tuesday. The Padres took a 4-3 lead with two runs in the eighth inning but allowed San Francisco to score twice in the bottom half.
The Giants (36-34) ended losing streaks of three games overall and four to San Diego.
"Every game we lose is tough," said Jesus Guzman, whose two-run shot in the eighth was one of San Diego's three homers. "... This was a game we had to win, but in this ballpark it's hard to beat those guys."
San Diego has not won a series at San Francisco since October 2010, but would have a good chance to end that drought if Stults (6-5, 3.28 ERA) performs well again.
The left-hander has allowed five earned runs over 31 innings in his last four starts while going 2-1. Stults walked only one batter in that span while holding opponents to a .167 average. He recorded his first complete game since 2009 versus San Francisco when he allowed two hits in a 2-1 victory over Arizona on Friday.
"The wide range of velocities keeps the hitters off-balance, disrupts their timing," manager Bub Black said. "He pitches. He truly pitches."
Stults has a 2.26 ERA while going 4-3 in his last nine starts, in which he's received an average 2.40 runs of support.
However, he's 0-1 with an 8.18 ERA in two outings against the Giants this season, though both came in April.
While Stults is 1-2 with a 5.84 ERA in five starts in San Francisco, Bumgarner (6-4, 3.30) has gone 2-0 with a 3.22 ERA in seven home starts versus San Diego - the Giants have won the last six. He gave up two runs and struck out 10 in six innings while not factoring in the decision of a 3-2 win over the Padres at AT&T Park on April 19.
The left-hander allowed two hits and also fanned 10 over seven innings of a 6-0 win at Atlanta on Friday - his second straight victory after a four-start stretch in which he was 0-3 with a 6.29 ERA.
"He really has been consistent all year, but this was up there as one of his best starts," manager Bruce Bochy said.
Brandon Belt had three hits with an RBI on Tuesday, and rookie center fielder Juan Perez delivered the go-ahead single in the eighth after throwing out a runner at the plate in the seventh.
In seven games since making his major league debut June 9, Perez is batting .421 (8 for 19) with three RBIs and has recorded four outfield assists.
"I've got to take advantage of every hour, every day I am here," Perez said. "Just keep it up, do what I'm doing on the field."
While Perez is likely to be in the lineup for the series finale, Giants shortstop Brandon Crawford will sit out after spraining two fingers on his right hand Tuesday.
San Diego's Logan Forsythe is 5 for 10 with a homer in the series. The second baseman is batting .417 with two home runs in his last six games versus San Francisco.