CINCINNATI -- The Chicago Cubs are headed to the postseason and Jon Lester is a big reason why. It was in the veteran left-hander's plans all along.

"I told (Cubs president Theo Epstein) in a meeting we had when the whole (contract) thing got going that I'm not here to grind through 2015," Lester said. "I wanted to make sure we're contenders. I didn't want to finish last and go through that again."

On Wednesday night, Lester capped his debut season in Chicago by retiring the final 20 batters he faced and center fielder Austin Jackson had a career-high five RBIs as the Cubs pounded the Cincinnati Reds 10-3 at Great American Ball Park

Lester (11-12) allowed one base runner over his final seven innings. He struck out nine and didn't walk a batter to lower his ERA to 3.34 in 32 starts.

"He was pretty much unhittable," said manager Joe Maddon. "That cutter is really nasty right now. He has everything playing right now. Yes, he's probably peaking at the right time."

Jackson had a pair of RBI doubles and second baseman Starlin Castro had four hits, including a homer, for Chicago (93-65), which won its fourth straight game to improve to 19-9 in September.

By virtue of the St. Louis Cardinals clinching the National League Central title Wednesday night, the Cubs now are certain to face the Pittsburgh Pirates in the NL wild card game on Oct. 7 either at Wrigley Field or PNC Park.

"The talent's here," Lester said. "Maybe we surprised ourselves a little bit. It's been a matter of teaching these young guys how to do it each and every day."

Cincinnati now lost 11 straight, equaling its longest losing streak since 1998.

The Reds collected just four hits Wednesday as the first year of their rebuilding project stumbles to its finish.

"We know it's ugly right now and it doesn't even look like baseball," said Reds manager Bryan Price. "There is no satisfaction from playing this poorly. These guys have to get through this and get better. We want to get back to the playoffs with this group."

Right-hander Anthony DeSclafani (9-13) made the 106th start this season by a Reds rookie and took the loss after allowing five earned runs in five-plus innings to finish off his debut season in Cincinnati.

"I guess it's been a good season overall," said DeSclafani. "I'm not happy with the way it ended. I had a couple goals in mind that I didn't reach. This will leave me with a solid taste in my mouth going into the off season. It will make me work harder next season."

Jackson capped his night with a bases-loaded single in the eighth inning to make the score 8-1, among 16 hits for Chicago.

DeSclafani struck out six of the first seven batters he faced. But the Cubs got to him in the third when Jackson delivered a two-run double to center for a 2-1 lead.

Anthony Rizzo doubled to left and scored on shortstop Addison Russell's single to center in the fourth to make it 3-1.

"The way we swung the bats and the at-bats we had, that set the tone for tonight," said Lester.

In the fifth, Jackson's second RBI double of the night drove home Lester, who singled, to give the Cubs a 4-1 lead.

Castro then belted his 11th home run of the season on DeSclafani's first pitch in the sixth to give the Cubs a four-run lead.

Castro had four hits in a game for the first time since 2013.

"He is playing with such tremendous focus right now," said Maddon. "He's playing a complete game of baseball."

It took time for Lester to find his rhythm Wednesday night. But after a rocky first inning, he settled down to close the regular season with an eight-inning gem.

"It was a good one to end on," Lester said. "But we're not finished. We've got a few more to go."

NOTES: LHP Jon Lester recorded his 203rd strikeout of the season in the fifth inning to set a Cubs season record for a left-hander. P Ken Holtzman had 202 strikeouts in 1970. ... Cubs LF Kyle Schwarber made his second start of the season in the leadoff spot on Wednesday. ... The Reds' lineup was minus 1B Joey Votto, who had upper back soreness, and 3B Todd Frazier suffered a slight strain of his right Achilles tendon in the third inning Tuesday while making a sliding attempt for a foul popup. ... OF Tyler Holt, claimed off waivers from Cleveland on Sunday, made his first start for the Reds on Wednesday in center field. ... Cubs CF Dexter Fowler has a career-high 100 runs, the most for a Cubs leadoff batter since Brian McRae scored 111 in 1996.