CHICAGO -- All eyes were supposed to be on Gregory Polanco. But thanks to his new-found success against left-handed pitchers, Anthony Rizzo stole the show.
Rizzo hit a two-run homer in the first inning off lefty Francisco Liriano, who came out in the fourth with discomfort on his right side. Rizzo also doubled and scored in the fourth and hit an RBI double in the seventh, a drive to deep right-center that struck Polanco's left wrist as the touted Pirates rookie tried to make the catch.
Rizzo has five home runs and a .344 batting average in 61 at-bats against left-handers this season. Last year, he batted .189 with seven homers against southpaws in 189 at-bats.
''I feel more comfortable against them now and it's the best I've ever hit left-handers at any level,'' Rizzo said. ''I don't know if I'll ever figure lefties out -- or right-handers, either -- but I do feel confident against them.''
Rizzo has every reason to feel confident. He has five homers in his last 10 games, raising his season total to 13.
''You can talk about mechanics and scouting reports and everything else, but the biggest thing in this game is confidence,'' Rizzo said. ''If you step into the batter's box with confidence, then you're giving yourself a much better chance to hit.''
Polanco went 1 for 5 after getting called up from Triple-A Indianapolis, where the right fielder was leading the International League with a .347 batting average and 49 RBI in 62 games.
''It was a lot of fun,'' he said. ''It was exciting. I was a little nervous at first but then I relaxed and had fun.''
Pinch-hitter Luis Valbuena's two-run double off Casey Sadler (0-1) broke a 3-all tie in the sixth and put Chicago ahead for good.
Travis Wood (6-5) allowed three runs and nine hits in 6 2-3 innings.
''It was a grind at times but I got through it,'' Wood said.
Andrew McCutchen hit a two-run homer for the Pirates, his ninth of the season and fifth in nine June games.
Valbuena and Junior Lake each had two hits for the Cubs, as did Pittsburgh's Russell Martin and Starling Marte.
Rizzo scored on a single by Starlin Castro in the seventh to push Chicago's lead to 7-3.
Rizzo's homer put the Cubs up 2-0, but the Pirates tied it on McCutchen's drive in the third.
In the top of the fourth, Rizzo led off with a double and scored on Darwin Barney's double. Pittsburgh tied it again in the bottom half on pinch-hitter Jose Tabata's RBI double.
''Rizzo's blast there in the first inning kind of got us rolling and we did a good job of adding on runs after that,'' Chicago manager Rick Renteria said.
Liriano allowed two runs in three-plus innings. He bent over and held his back after throwing a pitch to Rizzo, then left the mound after a few warmup pitches.
After leading the Pirates with 16 wins last season, Liriano has struggled this year. He is 1-6 with a 4.60 ERA in 14 starts.
Liriano will almost certainly miss his scheduled start Sunday in Miami and could land on the disabled list. Pirates right-hander Gerrit Cole (right shoulder fatigue) went on the DL on Sunday and second baseman Neil Walker (appendectomy) followed him Tuesday.
The Cubs released RHP Jose Veras, one week after designating him for assignment. He was 0-2 with an 8.10 ERA in 12 relief appearances while going 0 for 2 on save chances. ... Pittsburgh 3B Pedro Alvarez got the night off. He is 1 for 18 against Wood. ... Chicago RHP Jason Hammel (6-3, 2.53 ERA) is scheduled to start Wednesday night against RHP Brandon Cumpton (1-2, 6.51).