Reyes homered twice and had four RBI, Mitchell pitched five effective innings in his return from the DL and the Padres knocked off the playoff-contending Diamondbacks 6-2 Monday night.
"I just tried to take one pitch at a time and not really let things speed up," said Mitchell, who earned his first win since April 12, 2017. "It had been a while so that first inning was kind of different, but we were able to get out with one run, limit the damage there. I definitely settled in after that."
Mitchell (1-3) was sharp in his first start off the DL due to a right elbow impingement, holding the Diamondbacks to a run on two hits -- all in the first inning.
Reyes hit a three-run homer off Zack Godley (14-8) in the second inning and a solo shot off the right-hander in the fourth. Austin Hedges added a two-run single in the eighth inning for the Padres, who have won five of seven.
Reyes had his first career multihomer game and has homered in five of the past nine games to extend his hitting streak to nine games.
"He looks really confident in the batter's box," Padres manager Andy Reid said. "I can't really think of anybody in big league baseball who has as much pop or more pop than him."
Steven Souza Jr. had a run-scoring single in the first inning and Paul Goldschmidt an RBI double in the eighth for Arizona. The Diamondbacks were limited to five hits in their fourth loss in five games, dropping two games behind Colorado in the NL West.
"This is a group of guys that have done it before. They have done it this year at times," Diamondbacks manager Torey Lovullo said. "It obviously hasn't been as consistent as we have seen it. The same theme I have been talking about. Grind it out, keep getting after it, stay with the process. If it is not there for you, hand it off to the next guy."
The Diamondbacks returned to the desert after a difficult trip to Southern California. Arizona entered a four-game series with the Dodgers atop the division and left a game back after Los Angeles won three of four. All three loses came when the Dodgers rallied late, including Matt Kemp's two walk-off hits off Archie Bradley.
The Diamondbacks found themselves needing to rally after Godley walked the first two batters of the second inning and Reyes followed with a three-run homer to the pool deck in right-center to put San Diego up 3-1.
Godley gave up two hits for the second straight start, but both were home runs. He allowed four runs and struck out six in five innings.
"I felt like I made really, really good pitches," Godley said. "I made two bad pitches on the night. Both of them I paid for."
The Diamondbacks recalled RHP Yoan Lopez from Double-A Jackson and transferred 3B Jake Lamb to the 60-day disabled list. Arizona signed Lopez to an $8.27 million bonus coming out of Cuba in 2015, but he spent four seasons in the minors and at one time considered leaving baseball. The 25-year-old was 2-5 with 12 saves and led Southern League relievers in opponent average at .174. Lamb had season-ending left shoulder surgery last month.
Diamondbacks: Catcher Alex Avila had a foul ball bounce off the dirt and hit him in the throat in the third inning, but stayed in the game before being replaced by a pinch hitter in the seventh.
Diamondbacks LHP Robbie Ray has allowed three runs or less his past five starts heading into Tuesday's game against the Padres. San Diego LHP Joey Lucchesi is winless in four career starts against the Diamondbacks with a 7.71 ERA.
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