Rosales hit a go-ahead, two-run homer in the sixth inning and finished with four RBI, and rookie Ryan Schimpf scored three times to lead San Diego to a 5-2 victory against the Arizona Diamondbacks on Tuesday night.
"It's great to get the consistent playing time," Rosales said. "That's what you want to do in the major leagues. You want to play every day. I'm happy with the role I'm playing as a utility player, but it's really nice to get those consistent at-bats. You can make quicker adjustments when you play every day."
The start of the game was delayed 70 minutes by rain. It was only the seventh delay in Petco Park's 13-season history, the sixth because of rain. The other one was due to a swarm of bees during a game in 2009.
Arizona dropped into sole possession of last place in the NL West.
Paul Goldschmidt hit a tying, two-run homer for the Diamondbacks with two outs in the sixth off starter Paul Clemens.
Schimpf reached base for the third time when he drew a leadoff walk from reliever Zack Godley (4-4) in the bottom of the inning. Rosales homered to left field with one out, his 11th, to give the Padres a 4-2 lead.
"That's a big momentum shift and you want to come back right away," Rosales said. "You don't want to dwell on it. You want to come right back and answer back, and that's what we did."
Manager Andy Green said Rosales "has been outstanding. He's gotten limited opportunity this year and he's taken full advantage of all his opportunities. He's fun to watch play baseball."
Schimpf was hit by a pitch from Archie Bradley leading off the second and scored on Alex Dickerson's double. Schimpf walked leading off the fourth and scored on Rosales' sacrifice fly.
Rosales also hit a sac fly in the eighth to bring in Wil Myers, who doubled and stole third. It was Myers' 88th hit at home, a single-season record for Petco Park.
Keith Hessler (1-0) got the last out of the sixth for the win. Brandon Maurer pitched the ninth for his second straight save and 12th in 14 chances.
Clemens took a 2-0 lead into the sixth before being hit on his pitching hand by Jean Segura's comebacker and getting undone by two unearned runs. He recovered from the comebacker and threw out Segura, but with two outs, shortstop Luis Sardinas booted a routine grounder by Chris Owings. Goldschmidt then homered to left-center to tie it.
Clemens allowed two runs, none earned, and three hits in 5 2/3 innings. He struck out four and walked one.
Bradley gave up two runs and two hits in five innings, struck out seven and walked three.
"Kind of weird, only two hits, gave up two runs -- just a funny game sometimes," Bradley said. "You never know how things are going to affect you, but the hit-by-a-pitch and the walk came back to really hurt me tonight. I was honesty really pleased with staying composed the way I did in those two innings, coming back and striking guys out to get through the inning. But overall pretty pleased with it."
Diamondbacks: RHP Zack Greinke (12-7, 4.42 ERA) is scheduled to start the finale of the three-game series. He's 1-0 with a 3.54 ERA in three starts against San Diego this year and 7-1 with a 1.96 ERA in 15 career starts against the Padres.
Padres: RHP Luis Perdomo (8-9, 5.68), a 23-year-old rookie, is coming off his club-leading eighth victory, 3-1 at San Francisco on Sept. 14.