SAN DIEGO -- Padres pitcher Cory Luebke made a big mistake when he got Justin Upton mad.
It was a pair of quick pitches from Luebke that got the streaking Upton fired up and led to his first home run leading off the fourth inning.
"The guy quick-pitched me on the first pitch [of the fourth]," Upton said. "He did it on my first at-bat. It's just irritating, pitchers who are trying to trick the system. I'm just going to say it: You never see [Tim] Lincecum quick pitch me, Matt Cain, those guys don't do it.
"I got a good pitch to hit and I was mad about it."
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Upton homered again off Luebke (3-5) with two outs in the sixth to tie the game 2-all. The slugger also connected in a 6-1 victory Tuesday night in the series opener.
"They did it [quick pitch] Tuesday night against him and he hit a home run," Arizona manager Kirk Gibson said. "I know he doesn't like it. It kind of irritates him. He's hit two home runs after it, so hopefully they will do it again."
Upton reached 20 homers this season and extended his hitting streak to eight games. During the streak, he's batting .567 (17 for 30) with five home runs and 15 RBI.
"He's striking the ball well right now," Gibson said. "He's kind of carrying us right now. I hope it can continue."
Ian Kennedy (12-3) won his fourth straight start, limiting San Diego to two runs and four hits with nine strikeouts over six innings.
"Fastball command wasn't as good as I wanted it to be but my changeup was probably the best it's been in a while," Kennedy said.
Nady hit his fourth homer of the year off Luebke in the seventh to break a 2-all tie and send Arizona to its fourth straight win. The ball carried into the first row of the home run porch in right field near the 322-foot marker. Will Venable jumped for the ball but a fan caught it. TV replays appeared to indicate the fan didn't reach over the railing.
"I saw just one quick replay and it looked as though the ball cleared the wall," said Padres manager Bud Black, who briefly came out to discuss the play with first base umpire Kerwin Danley.
J.J. Putz pitched the ninth for his 22nd save in 26 chances. It was Putz's first appearance after missing 20 games with right shoulder tendinitis. He came off the disabled list Tuesday.
Luebke allowed four runs and six hits in six-plus innings. The rookie left-hander struck out six with one walk as he allowed more runs than in any of his previous five starts this season.
"You know Upton's hot going in. He was a guy I couldn't let beat me," Luebke said.
San Diego rookie catcher Luis Martinez made his first major league start memorable with his first hit, a solo homer in the seventh inning off Bryan Shaw to trim the Diamondbacks' lead to 4-3.
Luebke also had his first major league hit with an infield single in the fifth inning.
Arizona has won eight of 12 since the All-Star break to remain three games behind first-place San Francisco in the NL West.
The Padres lost for the fifth time in six games to fall a season-high 15½ games out of first.
Upton added to his home run barrage in spacious Petco Park with a deep drive in the fourth that carried to the back of the San Diego bullpen in center field before bouncing out into the picnic section.
Venable gave the Padres a short-lived 2-1 lead with a two-run triple in the fifth. Upton tied the game with a 433-foot, two-out homer in the sixth into the third deck of the brick Western Metal Supply Co. building in left field.
It was Upton's fourth career multihomer game and his first since June 21, 2010, against the New York Yankees.
Nady, a second-round draft pick of San Diego in 2000, put the Diamondbacks ahead for good in the seventh after Miguel Montero drew a leadoff walk.
Arizona leads the NL with 118 home runs. ... Sean Burroughs, the Padres' No. 1 draft pick in 1998, faced his old team for the first time and struck out as a pinch-hitter in the seventh inning. ... San Diego C Rob Johnson did not start after leaving Tuesday night's game with a bruised right hand after taking a foul ball off the back of his hand. ... Diamondbacks LF Gerardo Parra (sore left wrist) missed his third straight start.