CHICAGO -- The outing was a grind, but the result nonetheless vaulted Jon Lester ahead of his peers for the National League lead in wins.
"For whatever reason, the fastball command wasn't as good as the last couple of starts for me," Lester said. "For the last month, maybe longer, (the Reds) have been swinging the bats pretty well. They made me work and (got) into some deeper counts."
Lester still struck out five, walked none and threw 91 pitches for the victory. He has his highest win total since going 19-9 with the Boston Red Sox in 2010. He moved ahead of teammate Jake Arrieta and Washington's Max Scherzer, who each have 17 victories.
"He probably didn't have his better fastball today, but he was still very good," Cubs manager Joe Maddon said. "I've seen him a little sharper lately, but I think he knows when to put the foot on the gas a little bit. ... He was pitching very effectively. He was hitting his spots."
Chicago (96-55) won its second straight and is one away from matching last year's victory total. Cincinnati (63-88) dropped its second in a row and sixth in seven games.
Reds starter Josh Smith (3-2) gave up one run on three hits in three innings.
"(Lester is) a Cy Young candidate, and to get that opportunity to go against him and against that team is a huge opportunity for me and go out there and try to make the best of it," Smith said.
Lester was hit in the right wrist by a Joey Votto liner to lead off the sixth inning and had a visible welt but remained in the game.
"It's fine," Lester said. "My right hand, I don't need it. All that it's there for is to hold the glove. It'll be fine."
The Cubs never trailed en route to a 5-1 lead after five innings. Rizzo extended it to 6-1 in the sixth with a one-out base hit to drive in Fowler.
Lester and catcher David Ross combined for the Cubs' first run.
Ross singled to right with two outs in the second inning and rounded the bases to score on Lester's double to deep right-center.
The Cubs added four runs with two outs in the fourth against rookie reliever Wandy Peralta.
Fowler singled home Jason Heyward for a 2-0 Cubs lead. Lester, who reached on a walk and advanced to second on Fowler's hit, made it 3-0 when he scored on a Bryant double that started as a popup to short right and dropped in for a hit.
Rizzo's base hit to right scored Fowler and Bryant for a 5-0 lead. Peralta was pulled for a pinch hitter in the following inning after allowing four runs on three hits and two walks in his lone inning.
"The thing is about September and our situation is we're looking at some of the younger players that we brought up and (there are) sometimes painful lessons," Reds manager Bryan Price said. "It's hard to go through, but the only ways these guys are going to learn to pitch up here is to pitch."
The Reds broke the shutout with two outs in the fifth as Jose Peraza's triple to right-center brought home Steve Selsky.
NOTES: Reds manager Bryan Price said it was odd to watch ex-Reds LHP Aroldis Chapman close out Monday's game as a member of the Chicago Cubs. "I'm sure it was equally surreal (for him) to look across and see the Reds and be pitching against his old team," Price said. ... Following the Cubs series, the Reds head to Milwaukee for three games. They've beaten the Brewers in five of the last seven meetings. ... Since the All-Star break, 1B Joey Votto leads the NL with a .416 average entering Tuesday. ... Cincinnati RHP Josh Smith (3-1, 4.97 ERA) makes his sixth big league appearance on Wednesday as he faces off against the Cubs RHP John Lackey (9-8, 3.42 ERA). ... Cubs RHP Pedro Strop threw a simulated game on Tuesday and is expected to be activated from the disabled list (meniscus tear) on Friday. ... RHP Jason Hammel's 15th victory on Monday made him the fourth Cub with 15 or more wins, the first time Chicago has had that many since 1935 (Larry French, Bill Lee, Charlie Root and Lon Warneke).