SAN FRANCISCO (AP) -- It used to be a Madison Bumgarner start meant the San Francisco Giants almost assuredly would find the win column.
Now, still without a 2017 victory, MadBum just wants to get back in a groove and stop giving up costly home runs.
Jhoulys Chacin outpitched Bumgarner, Cory Spangenberg hit a go-ahead two-run homer in the seventh inning that chased the Giants ace lefty from his first home start in more than three months and the San Diego Padres beat San Francisco 5-2 on Thursday night.
Bumgarner (0-4) struck out five and walked one over 6 1/3 innings, taking his home mound for the first time since spraining his pitching shoulder in an April 20 dirt bike accident. The 2014 World Series MVP is yet to win after six 2017 starts.
"I gotta stop giving up home runs, that's not going to work," Bumgarner said. "I felt much better about tonight than the box score says. That's what's most frustrating."
Hunter Renfroe came off the disabled list and hit an early two-run homer to help back Chacin's third straight winning decision. Wil Myers added a run-scoring double in the eighth as San Diego bounced back from an embarrassing 18-4 rout by the Rockies on Wednesday at Coors Field.
Chacin (9-7) allowed two runs on four hits, struck out four and walked one in six innings.
Bumgarner received a warm welcome in his return, then went 1-2-3 in the first on 11 pitches, a pair of flyball outs to left and a strikeout. Then he surrendered a leadoff double to Jabari Blash to start the second, followed by Renfroe's homer just inside the left-field foul pole.
The left-hander pitched at AT&T Park for the first time since April 13. He was injured on a day off in Colorado, suffering a sprained AC joint in the shoulder and bruised ribs. He made his return to the big league mound nearly three months later in a start last Saturday at San Diego.
"He's a competitor, nothing he does really shocks me or anybody in baseball," Padres manager Andy Green said of Bumgarner's comeback. "He's good and even if it's not in midseason form for him he's still not an easy draw."
Bumgarner also allowed two home runs Saturday, so this marked the first time in his career he has surrendered multiple longballs in consecutive outings in the same season.
San Francisco fell to 0-6 in his starts, having given the ace just 10 runs of support.
"They're solid outings, we've just got to find a way to score a few more runs," manager Bruce Bochy said. "We had a couple chances there and it got away from us. I think it's encouraging he's healthy and he's throwing the ball I think very well."
The Giants wasted Denard Span's leadoff double in the fourth, stranding him at third with three straight outs after his hit. Span hit an RBI single the next inning that scored Gorkys Hernandez, aboard on a base hit. Eduardo Nunez singled home Span to tie the game at 2.
San Francisco loaded the bases against Brad Hand with two out in the eighth, but Buster Posey flied out to right.
Brandon Maurer allowed two singles in the ninth but finished for his 20th save. San Diego has won 15 of the last 20 meetings in the rivalry dating to last year's All-Star break.
Padres: C Austin Hedges, who went on the seven-day concussion disabled list Tuesday after taking a ball off the mask last Friday against the Giants at Petco Park, has what is considered a mild concussion. He just completed three days of hour-long sessions of vision training -- "It's really cool," he said -- because the main symptom he is experiencing is an inability to perceive the moving baseball. He felt far better Thursday and took some swings. He plans to catch a few bullpens before being eligible to return next Tuesday. … OF Manuel Margot was placed on the paternity leave list.
Giants: Nunez returned to the lineup playing third after he sat out Thursday's series finale against Cleveland with a tender left hamstring that has bothered him off and on this season.
Padres: RHP Trevor Cahill (4-3, 3.14 ERA) tries to win consecutive starts for just the second time this season after beating the Giants on Sunday his last time out. He is 3-1 with a 2.16 ERA and 41 strikeouts over his last six starts.
Giants: RHP Jeff Samardzija (4-11, 4.86) lost to the Padres on Sunday in his first outing after the break, but is 7-3 with a 3.68 ERA lifetime against San Diego.