SAN DIEGO -- For his first nine starts this season, Pittsburgh Pirates right-hander A.J. Burnett forged a 4-1 record thanks to a National League-best 1.37 earned-run average.

However, when Burnett finally stumbled Thursday night at Petco Park, the Pittsburgh offense came through.

"It's a nice little run the offense is on," Burnett said after the Pirates got homers from Jung Ho Kang, Gregory Polanco and Starling Marte and three-hit games from Andrew McCutchen, Neil Walker and Francisco Cervelli to power past the San Diego Padres 11-5.

The Pirates earned their seventh consecutive win behind a 15-hit attack.

"They came out swinging the bats tonight," Burnett said of his offense, which built a 6-0 lead through three innings. "Playing hard all the way around. This is fun to be a part of."

Pirates manager Clint Hurdle added, "We got out of the blocks early."

Burnett (5-1) allowed five runs (four earned) on eight hits and two walks in 5 2/3 innings. He struck out six, and his ERA climbed to 1.81.

While he was struggling, though, the Pirates were pounding Padres starter Ian Kennedy, who allowed seven runs on seven hits -- including the three Pirates homers -- and two walks in just 3 2/3 innings.

"This was a severe bump in the road," Padres manager Bud Black said of Kennedy, who fell to 2-5 as his ERA climbed to 7.15. "All his starts this season have been on a roller coaster."

"My command was all over the place," Kennedy said. "It's really, really frustrating."

Kang, Polanco and Marte all connected in the first three innings. Kang drove in the Pirates' first three runs. McCutchen and Marte each had two RBIs.

In seven starts since coming off the disabled list April 25 after recovering from a left hamstring strain, Kennedy has allowed 31 runs on 44 hits in 36 2/3 innings -- an ERA of 7.61. He has surrendered 12 home runs in 39 innings, or 2.8 per nine innings.

Kang, Pittsburgh's shortstop, gave the Pirates a 3-0 lead in the first with his 430-foot launch into the second deck in left. Second baseman Walker singled with one out and moved to second when Kennedy hit left fielder Marte on the left elbow with a pitch.

Kang crushed the first pitch he saw from Kennedy for his third homer.

"Big swing of the bat by Kang," Hurdle said.

Right fielder Polanco led off the second with his second homer, a 414-foot drive to center on a full-count pitch, to boost the Pirates' lead to 4-0.

Left fielder Marte followed a leadoff single by center fielder McCutchen in the third with a 377-foot drive to left on the first pitch from Kennedy to make it 6-0.

The Pirates built the lead to 7-0 in the fourth on a single by catcher Cervelli and a two-out, RBI double by McCutchen.

After the Padres took advantage of three Pirates fielding lapses to cut the margin to 7-4 -- and strand runners at second and third with one out in the fifth -- the Pirates scored four more runs in the sixth on run-scoring doubles by third baseman Josh Harrison and McCutchen and a two-run throwing error by Padres shortstop Alexi Amarista.

Left fielder Justin Upton started the first rally with a single and a steal -- becoming the first player in the major leagues this season with 10 home runs and 10 stolen bases. He capped the second rally with an RBI single that put two on and no one out. However, Burnett struck out left fielder Matt Kemp and catcher Derek Norris before getting second baseman Cory Spangenberg on a fly to center to prevent further damage.

"We could have defended better to help A.J. tonight," Hurdle said. "We probably could have eliminated some of the stress in the fourth and fifth innings."

NOTES: Padres RHP Brandon Morrow threw a three-inning simulated game Thursday, and he is scheduled to begin a rehab assignment Tuesday. Morrow has been on the disabled list since