(CHICAGO) – Willson Contreras wasn't happy with a called second strike in the second inning. He took his displeasure out on the next pitch, hitting it out of the park. Contreras homered and had three RBI, Jon Lester pitched five-hit ball through six innings and the Chicago Cubs beat the Atlanta Braves 8-3 Monday in a chippy matchup of NL division leaders. Jason Heyward added a solo homer for Chicago, which moved one game ahead of Milwaukee in the NL Central. Lester (7-5) allowed two unearned runs and struck out seven. The Cubs strung together five straight hits in a five-run fifth inning to break the game open. Kyle Schwarber doubled into the ivy to score Carlos Gonzalez. Kris Bryant, Anthony Rizzo, Javier Baez and Contreras followed with RBI. Tempers flared in the second inning when Contreras homered to right, giving the Cubs a 1-0 lead. Contreras turned to Braves catcher Tyler Flowers after the ball left his bat, and while rounding first base, gestured toward Atlanta's dugout and thumped his chest. Contreras and Flowers exchanged words as he returned to the dugout. Heyward escorted Contreras back to the dugout, and Braves pitcher Julio Teheran approached the third-base line. The benches cleared, umpire John Tumpane warned both teams and players congregated on the third-base line. No blows were exchanged. Teheran (5-6) was roughed up for the second consecutive start. Nick Markakis drove in two runs with a single in the sixth inning. Atlanta lost for the sixth time in 20 games.