CHICAGO -- Matt Szczur's exuberance as he rounded the bases perfectly matched the impact of his first career grand slam on Friday.
"I was super excited," he said. "I always want to contribute to the team and make an impact and it's great to do so in that manner."
Anthony Rizzo had given the Cubs a 2-1 lead with a bases-loaded single that scored Dexter Fowler, setting the stage for Szczur's slam.
Szczur sent an 0-1 pitch from Braves reliever Chris Withrow into the left-field bleachers to drive in Jason Heyward, Ben Zobrist and Rizzo as the Cubs (17-5) collected their fourth straight win and sixth in seven games.
The Braves (5-18) lost for the ninth time in 10 games.
"We're all happy for (Szczur)," said Cubs manager Joe Maddon. "He's kind of a managers', coaches' kind of dream player because he knows his role, he stays ready, he's good and he's very versatile. The last step for him was to really realize he belongs in the major leagues and can do this."
Pedro Strop (1-0) worked one inning of relief for the victory, while Jim Johnson (0-3) suffered the loss after pitching one-third of an inning to open the eighth.
Chicago starter Jon Lester (2-1) gave up a solo home run and little else but didn't get a decision as he left after seven innings with the scored tied at 1-1. Lester struck out 10 and walked two while allowing one run on seven hits.
"Jon Lester was outstanding today," said Braves first baseman Freddie Freeman, who homered off the Cubs left-hander in the fourth inning. "It's tough when he's got that cutter and his sinker command like he had today. He made the pitches when he needed to."
Braves right-hander Aaron Blair (0-1) also had no decision after being pulled for a pinch hitter in the seventh. He worked six innings and allowed one run on two hits while striking out three and walking three.
The Cubs had runners at second and third with two outs in the first inning but both were stranded when Blair got Jorge Soler on an inning-ending strikeout.
Freeman gave the Braves a 1-0 lead with his fourth-inning leadoff home run to right.
Blair, meanwhile, held the Cubs hitless until the fifth when Javier Baez bounced a lead-off double down the third-base line.
The Braves had the bases loaded with none out in the seventh. Lester walked Tyler Flowers in that inning, and Erick Aybar put down a bunt that Lester picked up but failed to throw to any base.
Maddon came out to talk to Lester at that point.
"I know the play can mess with your head a little bit, but you're still in good shape," Maddon said. "I wanted him to know that. I know you still have to process the moment but regardless of every level of experience, when something like that happens you'll get out of your normal thought pattern."
Braves reliever Alexi Ogando walked Rizzo and gave up a single to Soler to open the seventh. Both runners advanced when Baez bounced a grounder to second, and Addison Russell reached on an intentional walk.
But that threat was extinguished as Ross hit into an inning-ending double play.
NOTES: Cubs 3B Kris Bryant sat out Friday's game after suffering a mild right ankle sprain during Thursday's 7-2 victory over the Brewers. ...Friday's game in Chicago was the Braves' third in an eight-game, three-city road trip that started with a split in Boston and ends with three games against the Mets in New York. ... Atlanta entered Friday already holding a franchise record for losses in April (17) dating back to 1900. The Braves opened the season with nine straight defeats and dropped eight in a row between April 20-27. ... Friday was a homecoming for Braves catching tandem of Tyler Flowers and A.J. Pierzynski. Both formerly played for the Chicago White Sox. ... The Cubs have now outscored opponents by 79 runs (136-57). It is the largest differential on the big leagues, far ahead of second-place St. Louis. ... Cubs RHP Jake Arrieta's Thursday victory gave him a 21-1 record with a 0.89 ERA since June 21, 2015. ... The Braves send RHP Julio Teheran (0-3, 4.60 ERA) against Cubs RHP John Lackey (3-1, 4.97 ERA) in Saturday's middle game.