PITTSBURGH --- Suddenly, the ball has started flying off Andrew McCutchen's bat.

The center fielder and 2013 National League MVP doubled, homered and drove in three runs, and Charlie Morton allowed one run in seven innings as the Pittsburgh Pirates downed the Chicago Cubs 6-2 on Monday night.

The news wasn't all good, though, as Pirates second baseman Neil Walker underwent an appendectomy during the game. Tied for the team lead with 11 home runs, Walker could miss at least a month.

The Pirates will call up their top prospect, outfielder Gregory Polanco, from Triple-A Indianapolis on Tuesday. It is expected that Polanco will become the regular right fielder while Josh Harrison shifts to second base.

McCutchen has hit four of his seven home runs in his first eight games of June. His two-run shot in the third inning gave the Pirates a 3-0 lead, then he doubled in a run in the fifth.

Furthermore, he is having a big homestand. McCutchen is 7-for-15 with four extra-base hits through the first four games, including three against the Milwaukee Brewers. The Pirates have three games left in the series with the Cubs, and McCutchen is hitting .563 (9-for-16) against them season.

"Getting myself in a position to hit," McCutchen said of his power surge. "Made a little minor adjustment, now I'm seeing the ball a little longer and being able to get the barrel to it. When I get the barrel to it, good things happen. That's basically what I'm doing."

Morton (3-7) gave up six hits, did not walk a batter and struck out seven. He is 3-1 with a 1.83 ERA in his last four starts after losing his first six decisions, but was given an extra day of rest between starts so he could work with pitching coach Ray Searage. He is having better command of his trademark sinker.

"He had three major league pitches tonight," Pittsburgh manager Clint Hurdle said of Morton, who also mixed in a curveball and changeup. "He retired 17 guys on three pitches or less. The things we had seen from him before, he nailed every one of them on his to-do list tonight."

Pittsburgh left fielder Starling Marte and first baseman Ike Davis both snapped 0-for-23 slumps. Marte went 3-for-4 with two RBI doubles, the second of which made it 6-1 in the eighth and came two batters after Davis hit his fifth homer.

"It's fun to watch him swing the bat with some athleticism," Hurdle said of Marte. "We saw it before and though it might be a good game for him to get moving in a better offensive direction."

Right fielder Travis Snider and third baseman Pedro Alvarez had two hits each for the Pirates (30-33).

Shortstop Starlin Castro had three hits for the Cubs (25-36) and drove in both their runs with a seventh-inning double and a leadoff home run in the ninth, his eighth of the season, off reliever Jared Hughes.

"I'm feeling good right now," Castro said. "I feel strong. I know (Cubs manager Rick Renteria) wants to give me a day off but I'm feeling too good to sit on the bench right now."

Right-hander Edwin Jackson (4-6) allowed four runs and seven hits in six innings in taking the loss. He struck out eight and walked two but couldn't figure out how to get McCutchen out.

"He beat me on the same pitch twice," Jackson said, referring to his fastball. "I have to make better adjustments than that."

The Cubs lost their second straight game following a five-game winning streak. They also lost for 10th time in their 12 games at PNC Park, scoring a total of 23 runs.

NOTES: Pittsburgh 1B Ike Davis was back in the starting lineup and hitting cleanup a day after manager Clint Hurdle said 1B Gaby Sanchez would start three games in a row. Hurdle said he changed his mind because he thought the left-handed-hitting Davis gave his team a better chance against Cubs RHP Edwin Jackson than the right-handed-hitting Sanchez. ... Chicago OF Ryan Sweeney began a rehab assignment at Class A Kane County and went 0-for-2 with a walk against Cedar Rapids in a Midwest League game. He has been on the disabled list since May 3 with a right hamstring strain. ... Cubs LHP Travis Wood (5-5, 5.04 ERA) faces Pirates LHP Francisco Liriano (1-6, 4.54 ERA) on Tuesday night.