CHICAGO (AP) - When Chicago Cubs slugger Kyle Schwarber was lost for the season with a knee injury, Matt Szczur took on a new role as a reserve outfielder.
Szczur on Friday joined the long list of key contributors to the Cubs' best start in 109 years.
Szczur, a midgame defensive replacement, hit his first career grand slam during a five-run eighth inning and the Cubs broke away for a 6-1 victory over the Atlanta Braves.
Jon Lester struck out 10 over seven innings as the Cubs improved to 17-5, their top 22-game start since the 1907 team was 18-4.
"I can't explain the feelings I have," said Szczur, who has spent most of the past three seasons shuttling from Chicago to Triple-A Iowa.
It was 1-all in the eighth when the Cubs loaded the bases on two hits and a walk against Jim Johnson (0-3). Lefty Eric O'Flaherty relieved and gave up Anthony Rizzo's go-ahead single with one out.
Szczur followed by launching a fastball from Chris Withrow over the left field wall for his second home run this year.
Manager Joe Maddon called the 26-year-old Szczur "a manager's or coach's dream player."
"The last step for him was to really realize he belongs in the major leagues," Maddon said.
Freddie Freeman's solo shot in the fourth was only the Braves' fifth home run of the season. But in a matchup of the clubs with the best and worst records in the majors, the Braves fell to 5-18 amid missed opportunities.
Atlanta loaded the bases with no outs in the seventh, but Lester escaped. The lefty struck out two and got Nick Markakis on a grounder.
"Lester did a nice job to get out of that situation," Braves manager Fredi Gonzalez said. "You have a shot with Markakis. That didn't materialize."
Lester gave up seven hits and walked two. Pedro Strop (1-0) then pitched a perfect eighth.
Braves rookie Aaron Blair, in his second major league start, retired 11 straight batters and didn't allow a hit until Javier Baez's leadoff double in the fifth. Baez scored on David Ross' single.
Blair allowed two hits and three walks in six innings.
After snapping an eight-game skid in Boston on Thursday night, the Braves didn't get into their hotel rooms until 3:30 a.m., less than 10 hours before the first pitch.
And it was far from the Cubs' only advantage on a 44-degree, cloudy day.
While Maddon was asked before the game about Chicago's best start in more than a century, Gonzalez fielded a question about his job security with, "It's not like you're throwing games."
But their rebuilding effort has meant mighty struggles. The Cubs entered with an MLB-best plus-74 run differential, while Atlanta had scored 74 runs in all.
Yet it took an unlikely hero to put the Braves away.
"It was just hard," Szczur said of being sent to the minors five times last season. "because I knew if something happened I was the one going down."
Braves: Gonzalez remains optimistic CF Ender Inciarte (hamstring) will return from the disabled list next week. . 2B Gordon Beckham (hamstring) is healing faster. "Inciarte has been a month. I think Beckham won't take the full month," Gonzalez said.
Cubs: Kris Bryant (mild ankle sprain) was out of the lineup, but an MRI revealed no damage after he was hurt running the bases Thursday.
Lester's mental issues throwing to the bases flared again. Only this time he never threw it anywhere, allowing Erick Aybar's bunt to load the bases in the seventh.
Lester said he didn't freeze but instead "never had a handle on it." Maddon acknowledged they're trying to get him to "not worry."
Hip hop musician and producer Warren G was booed during a rushed performance of "Take Me Out to the Ball Game" in which he got some words wrong.
Tim Federowicz gets his first start behind the plate for the Cubs when he catches RHP John Lackey (3-1, 4.97 ERA) on Saturday. Federowicz was called up this week to replace the injured Miguel Montero. RHP Julio Teheran (0-3, 4.60) starts for the Braves.