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CHICAGO -- Darwin Barney was running as hard as he could, hoping his ball would fall into the gap.

Before he knew it, he had slowed down to a trot and a mob of teammates was waiting for him at home plate to celebrate his two-run homer in the bottom of the ninth that gave the Chicago Cubs an 8-6 win over the San Diego Padres on Wednesday.

"That was the first walk-off home run I've had at any level, I didn't even see it go out," Barney said. "I was just running, running hard. It was crazy. It's already gone and passed, it just happened so fast."

Barney launched an offering from Dale Thayer (0-1) into the left-center field bleachers to give the Cubs a three-game sweep.

James Russell (2-0) pitched a scoreless ninth to earn the win.

Carlos Quentin hit two homers and drove in four runs for the Padres. He had six extra-base hits and six RBI in the three-game series.

"I probably should have just drilled him or something," Cubs starter Ryan Dempster said, though he wasn't serious. "Really, looking back at it ... Holy cow. Fastball in on the black, he hits a homer, then fastball three balls outside and he hits a homer."

Chris Denorfia also hit a two-run homer for San Diego.

The Cubs tied the game in the eighth when pinch-runner Tony Campana stole second and third with two outs and scored on Starlin Castro's infield single.

Campana, who celebrated his 26th birthday on Wednesday, has seen little action over the last week as manager Dale Sveum looks for bigger power numbers out of the position.

"I'm going to come in and help the team as much as I can, when I can. That's kind of my job all the time," Campana said. "Whether I'm starting or coming off the bench, I'm just going to try to spark some excitement in the game."

The Padres came into the series last in the majors with 18 homers as a team and hadn't hit more than two in a game before hitting four on Monday.

Denorfia put the Padres on the board with a two-run shot off Dempster in the second, his second homer of the season.

Quentin followed suit in the third inning with a two-run blast to left-center, then went opposite-field in the fifth. It was his 15th career multihomer game.

Quentin, acquired from the Chicago White Sox in the offseason, missed the first 49 games of the season due to arthroscopic surgery on his right knee. He has six extra-base hits and six RBIs in his first three games with the Padres as their cleanup hitter.

"Right now I'm seeing the ball well and hopefully I continue to," Quentin said. "When you see the ball (this way) you do everything you can to take advantage of it."

San Diego starter Anthony Bass struggled with his control and couldn't make it through five innings. He was pulled after walking in a run with two out in the fifth -- his third walk of the inning.

Miles Mikolas walked in another run in relief before Alex Hinshaw came on to end the inning.

Bass was charged with five runs over 4 2/3 innings. He walked four and struck out two.

Dempster lasted just 4 1/3 innings and remained winless in nine starts on the year. He gave up six runs -- all on homers. He was pulled one batter after Quentin's second shot.

The Cubs bullpen combined for 4 2/3 scoreless innings.

"We don't win that game if they don't do the job they did," Dempster said.

In the second inning, Steve Clevenger knocked in a run with a single in his first at-bat since coming off the disabled list, then doubled in another run two innings later. He came up with the bases loaded and two out in the fifth but grounded out to second base.

Clevenger missed over a month due to a strained right oblique. He was 11 for 22 before going on the DL, and maintained a .500 average with a 2 for 4 day.

Game notes

Game time temperature was 59 degrees, a 31-degree difference from Monday's 90-degree opener. ... Padres OF Cameron Maybin (sprained right wrist) played for the first time since leaving in the sixth inning of Saturday's 9-0 loss to the New York Mets. Maybin pinch-ran for Quentin in the ninth. ... RHP Huston Street (right shoulder strain) threw a high-intensity bullpen session on Wednesday. He is expected to make his first rehab appearance on Friday with Class A Lake Elsinore against the Racho Cucamonga Quakes. ... Clayton Richard (2-6, 4.76 ERA) starts Friday for San Diego as the Padres a six-game homestand against Arizona. Paul Maholm (4-3, 4.62) will open a 10-game road trip for the Cubs on Friday in San Francisco.