Montero hit a two-run homer in the sixth inning, lifting the Diamondbacks past the Padres 3-1 on Saturday night and out of last place in the NL West.
The Diamondbacks started the season 8-22. With the win, they moved percentage points ahead of the Padres in the standings at 35-48.
"I guess it's good to get out of last place," Montero said. "I hope we continue like that and see where we are going."
Montero struck out against Eric Stults in his first at-bat but connected for his 11th home run next time up. The homer came on a changeup, something he had missed on in his earlier at-bat. When Stults tried to fool him later, Montero was ready.
"I put a good swing on that one," he said. "It was middle, middle-in, and sometimes those are pulled foul. But it stayed fair so I guess I stayed inside the ball very good."
Josh Collmenter (6-5) pitched 5 1/3 innings, giving up one run and five hits as Arizona won consecutive games for the first time since June 7-8 against Atlanta.
Addison Reed worked the ninth inning for his 19th save in 22 chances. He was the fourth Arizona reliever, a group which didn't allow a hit or run over the final 3 2/3 innings.
"I kind of wished I would have gone deeper in the game," Collmenter said. "But the bullpen did a great job tonight."
Diamondbacks manager Kirk Gibson saluted his bullpen as well, and noted it was a typical game at Petco Park.
"It's hard to score in this park and we played just well enough to win," he said.
It was difficult for Padres manager Bud Black to accept the loss, the Padres' third straight defeat.
"One bad pitch," Black said of Stults' offering to Montero. "Tried to get a changeup down and away and he just missed his spot."
Stults (2-11) became the majors' leader in losses, with an NL-high 5.36 ERA. He also went 5 1/3 innings and yielded three runs -- two earned -- while giving up just three hits. Stults walked three for the second straight game and stuck out two in losing his career-high sixth consecutive start.
Paul Goldschmidt was aboard for Montero's homer, after walking and reaching second on a botched double-play attempt.
Martin Prado grounded to Chase Headley, but his throw to second baseman Alexi Amarista was high, with Goldschmidt being safe. Amarista retired Prado at first, a play which was challenged by Gibson but upheld.
"I just got underneath it a little bit and it sailed," Headley said. "Lexi did a great job to make a play and get an out still."
The Diamondbacks tied the score in the third inning, thanks in part to an error by Rivera. Ender Inciarte singled and stole second, advancing to third when Rivera's throw was off line. Inciarte scored on Prado's one-out sacrifice fly.
The Padres threatened in the fifth inning when Rivera led off with a single and moved to second base on a sacrifice bunt by Everth Cabrera. But Amarista flied out and Stults struck out.
Diamondbacks SS Chris Owings remains out of the lineup with a sore left shoulder. Owings is expected to have it examined on Monday. . OF Mark Trumbo has started to run the bases in his comeback from a broken left foot. . Gibson had no update on when RHP Bronson Arroyo (sprained right elbow) would return. . Padres OF Carlos Quentin (sore left shoulder) is likely unavailable until next week. . RHP Andrew Cashner (sore right shoulder) has yet to resume throwing. . The Padres had gone eight straight games without allowing a home run before Montero's two-run blast. . Diamondbacks RHP Michael Bolsinger (1-3, 4.78) faces Padres RHP Odrisamer Despaigne (1-0, 0.00) in Sunday's series finale.