PITTSBURGH (AP) -- Edwin Jackson pitched just three innings Thursday before being removed following a long rain delay. That was long enough for the Cubs right-hander to absorb another loss.

Jackson gave up two runs in the first inning and two more in the second as the Pittsburgh Pirates beat Chicago 4-2, the Cubs' fourth straight loss.

Jackson (1-7) has a 6.11 ERA through 10 starts.

"I got beat with men on base with balls up in the zone," he said. "I had some times when I got it down but in vital situations when I needed to keep the ball down, I wasn't doing that, and that pretty much sums up the game."

Jackson is in his first season with the Cubs after signing a four-year, $52 million contract over the winter as a free agent.

"I think at times he tries too hard to justify his contract and overthrows," Chicago manager Dale Sveum said. "I think he needs to relax and just be Edwin Jackson, the guy we liked enough to sign."

Jackson had pitched better in his previous two starts, going 1-1 while allowing five runs in 12 innings. He has yet to show any consistency with one-third of the season nearly over.

"You wish you knew what happens in those situations, why the same guy doesn't come out all the time," Sveum said. "He seems like he doesn't come out with a lot of conviction early in games."

The Pirates won their fourth in a row as Andrew McCutchen had three hits and two RBIs.

Leadoff hitter Starling Marte singled and scored in each of the first two innings as Pittsburgh built an early 4-0 lead. The Pirates moved a season-best 11 games over .500.

Reliever Vin Mazzaro (3-0) pitched 2 1-3 scoreless innings. He replaced starter Jeanmar Gomez in the fourth inning following a rain delay of 1 hour, 47 minutes.

Gomez allowed one run and three hits in 3 2-3 innings.

Jason Grilli pitched a 1-2-3 ninth inning and is a perfect 19-for-19 in save opportunities.

Marte led off the bottom of the first inning with a single, stole second with one out and scored on McCutchen's single. McCutchen stole second and scored on Michael McKenry's single.

Marte singled in the second and scored on Travis Snider's triple that rolled to the 410-foot notch in left-center field. McCutchen added his second RBI single.

The Cubs got a run in the fourth when David DeJesus led off with a double and scored on Anthony Rizzo's grounder. The Cubs had runners on the corners when two outs when play was halted, but Mazzaro got Welington Castillo to hit an inning-ending groundout after the delay.

Chicago cut the deficit to 4-2 in the seventh with Darwin Barney singling in Castillo, who had walked.

Jackson was struck in the rear end by a line drive off the bat of Marte in the second inning. Shortstop Starling Castro jammed his right ankle while being thrown out trying to stretch a single into a double in the sixth inning by Snider, the right fielder. Both Chicago players were able to stay in the game.

"I'm a little sore but I'm good," Castro said.

NOTES: Rizzo's struggles continued as he was 0-for-4, dropping him to 6 for 41 (.146) in his last 10 games. ... The Cubs' road trip continues Friday night at Cincinnati with RHP Scott Feldman (4-3, 2.19) facing Reds RHP Bronson Arroyo (4-4, 3.28).