PHOENIX -- Adam Eaton wreaked some havoc with his speed Wednesday night.
"Triples are always fun," said Eaton, who is hitting .267 with two doubles and the triple since his debut on September 4.
With the Diamondbacks trailing 2-1, John McDonald reached on an infield single to start the fifth, went to second on a sacrifice and scored on Eaton's triple to left-center field - his first career RBI in 44 at-bats and his first career triple.
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"Usually the left-center field gap is the hardest place to get a triple, or maybe down the left-field line," Eaton said. "If you can get a triple to the left-center field gap you've got the horses going a little bit."
Eaton scored when Edinson Volquez was called for a balk for starting his motion, shifting his left foot back before taking his right foot off the rubber.
"I was creeping down the line and thinking about going [stealing home] if he went into his normal motion," Eaton said. "I think he got flustered and stepped off with the wrong foot."
Volquez said he thought the umpire had called time.
"It was a bad inning. Just one inning," Volquez said. "I was under control the whole game but that one inning I gave up a few runs and that was the whole game."
Justin Upton and Paul Goldschmidt hit consecutive doubles to make it 4-2.
"I got a couple of pitches up in the zone I could hit and got the barrel on them," said Upton, who is hitting .320 with three doubles and two homers during his past seven games.
Dan Wheeler also had an RBI triple and Miguel Montero added a run-scoring double for the Diamondbacks, who have won three straight. Arizona remained 4 1/2 games behind St. Louis for the second NL wild card.
"We were seeing good pitches and not missing," Upton said. "That's how the offense gets going."
The Diamondbacks are .500 since they were 64-64 on August 26.
Arizona starter Trevor Cahill (12-11) went six innings, allowing two runs and five hits with four walks and four strikeouts. Two of his walks and four of his baserunners came in the Padres' two-run third.
"He certainly has the experience," said Arizona manager Kirk Gibson. "You have to minimize [the runs allowed]. He walked two guys and they scored. The rest of the game was clear for him."
Max Venable and John Baker had consecutive RBI singles for the Padres, who have lost two straight to the Diamondbacks after winning eight of their previous nine against them.
"We didn't get as many baserunners tonight as we have over the last couple of months," said Padres manager Bug Black. "It came down to that three-run inning. They strung together some hits and we didn't. They bunched them together that inning."
Volquez (10-11) gave up four runs and eight hits over six innings. He struck out five and did not walk a hitter for the first time since Sept. 25, 2006 for Texas against the Los Angeles Angels, a span of 108 starts.
San Diego took a 2-0 lead in the fourth when Venable and Baker hit two-out run-scoring singles after Cahill had issued one-out walks to Carlos Quentin and Yonder Alonso.
Montero made it 2-1 in the bottom of the inning when he doubled home Upton, who led off the inning with the first of his two doubles.
Arizona made it 6-2 in the eighth when Brad Boxberger hit Montero with a pitch, Wheeler tripled and second baseman Logan Forsythe's relay throw sailed into the Diamondbacks dugout to allow Wheeler to score.
Diamondbacks reliever Brad Ziegler induced his 18th double-play grounder of the season, the most by a relief pitcher in the majors since Jeremy Affeldt also recorded 18 GIDPs in 2009 for San Francisco. ... Goldschmidt became the fifth Arizona player - and first since 2008 - with 40 doubles in a season. ... Quentin, playing for the first time since Sept. 10 because of pain in his surgically repaired right knee, left the game in the fourth after going 1 for 2. Black said Quentin "was a little uncomfortable.". Cahill joined C.C. Sabathia as the only pitchers since 1990 to record 10 wins and 30 starts in each of his first four seasons.. Padres RHP Andrew Cashner, who gave up six runs in 3 2/3 innings on Friday, told reporters Wednesday he's done for the season with lingering soreness in his right lat muscle. Cashner finishes the season 3-4 with a 4.37 ERA in 32 games and five starts. ... San Diego CF Cameron Maybin missed his second straight game with a sore left Achilles tendon. ... Before the game, the Diamondbacks recalled OF A.J. Pollock from Triple-A Reno and also selected the contract of INF Mike Jacobs from Reno. Arizona designated OF Cole Gillespie for assignment to make room on the 40-man roster for the 31-year-old Jacobs, who served a 50-game suspension in 2011 and into the start of 2012 for using HGH. "He did his 50 games," Gibson said. "He played the season in Triple-A and was a good leader down there." ... LHP Tyler Skaggs (1-2) will look to snap a two-game losing streak when he takes the mound for Arizona against Padres LHP Clayton Richard (13-12) in a getaway day afternoon game Thursday. Richard is 5-0 with a 3.80 ERA in eight career starts against Arizona.