PITTSBURGH -- Ben Zobrist hit a three-run homer, Anthony Rizzo had a solo shot among his three hits and Jon Lester worked out of a pair of jams while pitching 5 2/3 scoreless innings as the Chicago Cubs beat the Pittsburgh Pirates 6-2 on Wednesday to complete a three-game sweep.

Zobrist's home run in the third inning opened the scoring and came immediately after center fielder Andrew McCutchen dropped Rizzo's two-out liner for an error to extend the inning, sending the Cubs on their way to their seventh win in eight games.

Chicago improved its major-league-best record to 20-6 while winning its seven consecutive road game. The Cubs completed their first sweep in Pittsburgh since Sept. 7-9, 2012 and moved six games in front of the second-place Pirates (15-13) in the National League Central.

The Cubs have a 13-2 record against division opponents.

Lester (3-1) scattered eight hits, struck out five and walked two, lowering his ERA to 1.58. The left-hander has allowed one run or less in five of his six starts this season.

The Pirates loaded the bases in the fourth and put runners on first and second in the fifth -- both times with no outs -- but failed to score in either inning as they lost their fourth straight game following a six-game winning streak.

Rizzo doubled and scored on Javier Baez's double in the fifth inning then hit a solo home run, his ninth, in the seventh to extend the Cubs' lead to 5-0. He scored three times and finished the series with six extra-base hits -- five doubles and the home run.

Rizzo is hitting .362 (17-for-47) with 16 RBIs in his last 12 game after hitting .163 in his first 14. He is also batting .442 (23-for-52) in his last 13 regular-season games at Pittsburgh with nine doubles and nine RBIs.

Baez also had three of the Cubs' 12 hits and drove in the game's final run with a fielder's choice grounder in the ninth. Addison Russell added two hits and Kris Bryant ran his hitting streak to 10 games.

Matt Joyce accounted for the Pirates' scoring with a two-run pinch-hit home run in the seventh inning. It was his fourth, three of which have come as a pinch-hitter.

Juan Nicasio (3-3) had won his first three home starts after being signed as a free agent in the offseason but lasted just 4 1/3 innings. He allowed four runs -- one earned -- and eight hits with three walks and three strikeouts.

Pittsburgh got two hits each from McCutchen, David Freese and Josh Harrison. McCutchen had gone 2-for-19 in his previous five games.

NOTES: Cubs RF Jason Heyward (sore right wrist) was not in the lineup for a third consecutive game but may be ready to play Thursday night against Washington in the opener of a four-game series at Chicago. ... Cubs 3B/OF Kris Bryant started in the outfield for a fourth straight game, playing left field for third time in that span after playing right field on Tuesday night. ... Pirates rookie C Elias Diaz underwent right elbow debridement surgery Tuesday and is expected to be sidelined until mid-July. ... RHP Kyle Hendricks (1-2, 3.52 ERA) will start for the Cubs against Nationals RHP Joe Ross (3-0, 0.79 ERA) on Thursday night. ... The Pirates are off Thursday, then will start LHP Francisco Liriano (2-1, 3.86 ERA) on Friday night against Cardinals RHP Carlos Martinez (4-1, 2.60 ERA) in the opener of a three-game series at St. Louis.