Blum hit a go-ahead, two-run homer in the seventh inning and Peavy was brilliant again with 11 strikeouts, leading San Diego to a 3-1 win against Arizona on Monday night that trimmed the Diamondbacks' lead in the NL West to two games over the Padres.
It was the first of seven games between the division's top two teams in 10 days. After this four-game series, the teams will play three in Phoenix starting next Monday.
"This is a huge series for us, and we know that," said Peavy, who outdueled Livan Hernandez and improved to 10-2 in 13 starts following a San Diego loss this season. "We're playing catch-up. We're on top of the pack in the wild-card race, but we're not focused on that. We want to be division champions and we feel like we can do that."
Milton Bradley also homered for San Diego, which is trying to win its third straight division title. The Padres retained a three-game lead in the wild-card race over Philadelphia, which beat the New York Mets 9-2.
"The later in the season you go, the more energy it seems that each game has," said Arizona manager Bob Melvin, who sends out reigning Cy Young Award winner Brandon Webb on Tuesday night against Justin Germano. "With those two pitchers on the mound pitching as well as they did, yeah, if felt like there was some energy."
The Padres won for the fifth time in seven games, including going 4-2 on a trip to New York and Philadelphia.
"What a big night for the boys, for us coming off a great road trip, to come from behind," Peavy said.
Peavy (15-5) tied his career high in victories. He struck out 11 for the third straight start and reached double digits for the eighth time this year, pushing his NL lead to 197.
Peavy also became the Padres' career leader in strikeouts. His first-inning punchout of Orlando Hudson was No. 1,037, moving him past Andy Benes. Peavy struck out seven straight from the second to the fourth inning.
"The game was on the line there," Peavy said. "Most of the time you don't cut it loose in the second inning, but I had to do all I could do to keep Conor Jackson from scoring there because I expected the game to go as it did."
Peavy and two relievers combined on a five-hitter. Trevor Hoffman pitched the ninth for his 34th save in 39 chances, and the 516th of his career.
Hoffman, who blew two saves last week against the Mets, retired Eric Byrnes on a groundout to shortstop to open the inning before allowing consecutive singles to Jackson and Stephen Drew to put runners on first and third. Hoffman got Jeff Salazar to pop up to shortstop and struck out Montero to end it.
Blum's shot with two outs in the seventh boosted Peavy to his sixth straight winning decision. With the Padres trailing 1-0, Blum hit a full-count pitch from Hernandez (9-9) into the seats in right field, his third. Josh Bard was aboard on a walk.
Blum laid off a few breaking balls to get the count to 3-2.
"He just happened to leave a fastball over the plate 3-2 and I got a hold of it," Blum said.
Peavy called Blum "an unsung hero," and the utility infielder has been solid since getting the bulk of the starts at second base in the second half in place of struggling Marcus Giles.
"I appreciate that," Blum said. "We're doing all we can to win ballgames. If it wasn't for Jake leaving only one run on the board for us to come back and win the ballgame, who knows what would have happened."
Bradley added a solo shot off Juan Cruz with two outs in the eighth, his ninth with San Diego and 11th overall.
Peavy's only mistake was a 2-2 slider that Byrnes drove into the first row of the second deck in left field with one out in the sixth. It was Byrnes' 19th.
"Peavy was lights-out tonight," Byrnes said. "He was throwing and hitting off the corners all night. It was tough. He didn't make many mistakes."
Peavy allowed one run and three hits in seven innings, with three walks. He also had two singles.
Hernandez also went seven, allowing two runs and six hits with three strikeouts and one walk. Hernandez dropped to 0-3 in five games at Petco Park and 10-4 overall against the Padres in 21 career starts.
- Padres All-Star RHP Chris Young was encouraged after throwing a bullpen session and is cautiously optimistic he can start Thursday or Friday. The 6-foot-10 right-hander was forced to leave his start against the Mets on Tuesday night after five innings because of lower back pain. He returned to San Diego to have his back checked and missed his scheduled start Sunday at Philadelphia.