SAN DIEGO -- Jorge Lopez couldn't hide his excitement.

"At first, it was like, 'here I am,'" the 22-year-old right-hander said Tuesday night after he won his major league debut with the Milwaukee Brewers, 4-3 over the San Diego Padres at Petco Park.

"It's been great," Lopez continued. "It was amazing. I'll take the win."

Brewers shortstop Jean Segura's two-run homer in the sixth inning was the difference for Lopez, the Brewers' second-round pick in the 2011 draft. He allowed three runs on eight hits and two walks in five innings. He had seven strikeouts and threw 94 pitches with 59 going for strikes.

"Their rookie was outstanding," Padres manager Pat Murphy said after Lopez bested Tyson Ross (10-12) in the Padres right-hander's last start of the season.

Lopez was the Double-A Southern League Pitcher of the Year with a 12-5 record and 2.26 ERA for Biloxi.

"He did a nice job," Brewers manager Craig Counsell said.

The difference came on only the ninth homer allowed by Ross this season.

Segura, who doubled home a run in the first inning, hit a 363-foot drive off the second balcony of the Western Metal Supply Co. building in left to erase a 3-2 Padres lead. Brewers' left fielder Kris Davis had opened the inning with a single off Ross.

Right-hander Francisco Rodriguez picked up his 38th save for the Brewers.

The Padres spotted Milwaukee a two-run lead in the first before taking a 3-2 lead.

Brewers second baseman Scooter Gennett opened the game with a single to right off Ross, advanced to second on an infield out and scored on first baseman Adam Lind's single to center. After a walk to Davis, Segura drove Lind home with a bad-hop double over the head of Padres third baseman Yangervis Solarte.

"I didn't have a good rhythm early," said Ross. "It's hard to find your tempo with runners on base."

The Padres halved the deficit in the third when Solarte hit a two-out single, advanced to second on a wild pitch and scored on right fielder Matt Kemp's single to center. The RBI was Kemp's 100th of the season.

The Brewers' got a break when Justin Upton's ensuing line drive into the left-field corner bounced over the wall for a ground-run double, forcing Kemp to stop at third.

"If that ball stays on the field, Kemp scores and it might have been a different game," said Murphy.

Second baseman Cory Spangenberg opened the Padres fourth with a triple into the right-field corner. Catcher Austin Hedges followed with a walk ahead of Ross' bloop single to left for his sixth RBI of the season.

First baseman Will Myers' put the Padres ahead with a line-drive single to center, although Lopez avoided further damage by getting Solarte to ground into an inning-ending double play.

Ross allowed four runs on six hits and three walks with seven strikeouts in six innings.

NOTES: Padres RF Matt Kemp departed Tuesday's game with soreness in his right wrist shortly after driving in his 100th run of the season. "It started irritating me the other day when I was swinging," said Kemp. "Every time I swing, I feel a little pain." ... RHP Jorge Lopez became the 12th player to make his major league debut for the Brewers this season. ... 3B Yangervis Solarte returned to the Padres starting lineup Tuesday after missing four starts with a tight right hamstring.