PITTSBURGH -- The Chicago Cubs believe Edwin Jackson can be a big part of their future, which is why signed him to a four-year, $52 million contract as a free agent in the offseason.
However, the right-hander isn't helping them very much in the present.
The right-hander lost again Thursday, giving up four runs in three innings as the Pirates beat the Cubs 4-2 at PNC Park to complete a three-game series sweep.
Jackson (1-7) was rocked for four runs and six hits in three innings. He did not return after a one-hour, 47-minute rain delay in the fourth inning.
"Today I got beat with men on base with balls up in the zone," Jackson 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.
"Most of the balls I got hurt on were up in the zone. I've got to do a better job of keeping it down."
Jackson had pitched decently in his previous two outings, allowing five runs in 12 innings while going 1-1. He also had six strikeouts against the Pirates and only one walk.
But Jackson has a 6.11 ERA through 10 starts.
Chicago manager Dale Sveum could only shake his head when asked why Jackson has been so inconsistent.
"You wish you knew what happens in those situations -- why the same guy doesn't come out all the time," Sveum said.
Andrew McCutchen had three hits and two RBIs to help the Pirates to their fourth straight win, pushing a season-high 11 games above .500 at 29-18. Starling Marte added two hits.
"We're playing good baseball and I don't think we've reached our ceiling yet," McCutchen said. "The pitching has been good all year, but the hitting has kind of been up and down. The bats are eventually going to come around and we should be even better when that happens."
Vin Mazzaro (3-0) pitched 2 1/3 innings in relief of starter Jeanmar Gomez for the win. Gomez gave up one run and three hits in 3 2/3 innings.
"I knew I was coming in to pitch about a half-hour before the delay ended, but you never know for sure what's going to happen when it rains and I tried to stay as prepared as possible," Mazzaro said. "Jeanmar was pitching well and I was glad to come in and pick him up."
Jason Grilli notched his 19th save in as many chances by pitching a perfect ninth.
Marte singled and scored in each of the first two innings as the Pirates opened a 4-0 lead.
Marte led off the first with a single, stole second and scored a single by McCutchen. After McCutchen stole second, Michael McKenry hit an RBI single.
In the second, Marte singled with two outs and scored on Travis Snider's triple. McCutchen then drove in Snider with a single.
The Cubs held the Pirates scoreless the rest of the way but managed just two runs.
Chicago's David DeJesus led off the fourth with a double and scored on Anthony Rizzo's groundout. In the seventh, pinch-hitter Ryan Sweeney hit an RBI single that drove home Welington Castillo, who walked.
"We're going to be a better team as we keep getting more experience, become a good team like the Yankees and the Pirates," Cubs shortstop Starlin Castro.
NOTES: The Pirates plan to wear Pittsburgh Penguins jerseys while traveling on their two-city road trip that begins Friday night at Milwaukee and includes a stop in Detroit. The NHL's Penguins hold a 3-1 lead over Ottawa in their best-of-seven Eastern Conference semifinal series in the Stanley Cup playoffs. ... RHP A.J. Burnett (3-4, 2.57) is scheduled to pitch for Pittsburgh on Friday night against RHP Marco Estrada (3-2, 5.44). ... Chicago RHP Scott Feldman (4-3, 2.19) will try to run his winning streak to five games on Friday night when he pitches against Reds RHP Bronson Arroyo (4-4, 3.28) at Cincinnati in the opener of a three-game series.