CHICAGO -- Cubs catcher Willson Contreras was more animated, hopping up out of the crouch and giving a celebratory fist pump on Tuesday night. All Alec Mills allowed of himself as he walked off the mound was a subtle slap of his glove.

The moment arrived after three consecutive sliders, which were each enticing enough to generate a feeble swing from Reds slugger Nick Castellanos. The quick strikeout ended the top of the fifth, stranded a pair of runners and set the Cubs on course for a 3-0 victory at Wrigley Field.

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"I just went right at Castellanos," Mills said. "Threw three pretty good sliders. Big strikeout. Needed that."

As the National League Central-leading Cubs (25-18) continue their march toward October, Mills' six-inning showing was a much welcomed performance. Chicago knows it will be leading hard on its one-two punch of Yu Darvish and Kyle Hendricks, but there is still the matter of shoring up the rest of the staff.

Hendricks and Darvish have combined for a 2.50 ERA with a 7.6 strikeout-to-walk ratio in 108 innings this season. The rest of the rotation has turned in a 5.43 ERA with a 2.3 strikeout-to-walk ratio in 117 2/3 innings, including Mills' showing against Cincinnati.

Mills and veteran lefty Jon Lester have been battling through rough patches. José Quintana and Tyler Chatwood are on the 10-day injured list and working through throwing programs. Rookie Adbert Alzolay is the next man up for the No. 5 spot.

The postseason is only three weeks away.

"I try not to think about that, yet," Mills said. "Right now, we just need to win the game we play today. I think guys will sort some things out. I think right now, we're struggling a little bit as a rotation outside of those two guys.

"But, at the same time, we know how to pitch. We know how to get outs. I think it's going to turn around. We'll be ready to go later in the season."

Mills was trusted with a job in the Opening Day rotation, and circumstances have dictated allowing the right-hander to work his way through recent struggles. On a brisk night -- with the flags rattling their poles around the ballpark as the wind howled in -- Mills found a rhythm and kept Cincinnati's lineup quiet.

"Getting another great start from a starter for us goes a long way," Cubs manager David Ross said. "We get the lead to [the starting pitchers] early, those guys can be a little more aggressive, especially with the environment. Attack the hitters."

The environment turned Wrigley Field from a hitter's haven into a pitcher's park on Tuesday, when the steady wind off Lake Michigan was coupled with a misty rain. Pitchers plan for an opposing lineup by poring over scouting reports, but there are also strategies that involve factoring in the conditions.

"Definitely, that's an element," said Ross, who caught plenty of ballgames at the Friendly Confines in his career. "That's an element that is unique to Wrigley."

Mills summed up part of the approach.

"Hey, here's a fastball. See how hard you can hit it," the pitcher said. "A lot of times, they're not going to be able to get it out of the yard and maybe not do as much damage."

One of those situations arrived in the third inning, when Mills fired a sinker to Castellanos. The Reds outfielder crushed the ball to center field and, according to Statcast, the ball in flight would have been a homer in nine MLB stadiums. On this night, it was caught on the edge of the warning track by Ian Happ.

The Cubs had similar instances, including a deep flyout to left in the sixth from Javier Báez, who Ross said shouted, "Wrigley!" to the heavens after the catch. David Bote (two RBIs) and Báez (one) defied the elements with two-out, opposite-field triples in the second and third, respectively, off Tyler Mahle to give Mills his lead.

In his third start of the year against the Reds, Mills focused on his four-seamer first (49 out of 102 pitches), turning to his sinker as the secondary fastball. He worked in the slider more than usual -- getting five whiffs on five swings -- and balanced it all out with his changeup and curve (65.2 mph at its slowest).

"Little adaptations," Mills said of adjusting after facing Cincinnati multiple times. "Little changes here and there can do big things, as far as different fastballs, different parts of the zone, up and down. I think that was kind of an emphasis just for me tonight -- to change a little bit up."

Mills' effort came after a gem from Hendricks on Monday and on the eve of Darvish's Wednesday battle with Cincinnati's Trevor Bauer.

The Cubs will need more starts like it, too.

"That was a beautiful game," Cubs reliever Duane Underwood Jr. said. "And we needed it as a team. These are some big games we've got lined up."