Chicago will start Randy Wells in the finale, and Cincinnati will counter with Bronson Arroyo.
Chicago's winning trend began with a win over St. Louis and includes a four-game sweep of Pittsburgh. Chicago had lost five straight games immediately before the streak and is 12-10 since the All-Star break.
"We're still playing and have pride in what we do," said veteran first baseman Carlos Pena. "We prepare and work hard, and it's nice to see actual results come our way and reap the benefits of hard work. It's very rewarding when you put in your work and at the end of the day get a win."
The Reds, meanwhile, are 9-12 since the break, and they've seen their distance in the standings double. Cincinnati was just four games out of first at the season's intermission, and 8 1/2 games behind first-place Milwaukee prior to Saturday's loss. The Reds are 24-32 on the road this season.
Arroyo has gone 77-69 with a 4.14 ERA in five-plus seasons in Cincinnati's rotation, and he went into the 2011 season with back-to-back years of winning records and better-than-average ERAs. The right-hander has struggled this year, though, and he's posted an 0-3 record and a 7.42 ERA in his last five outings.
He also had a similar run -- six starts, an 0-3 record and a 7.64 ERA -- in May.
Wells went six innings and earned the victory in his most recent outing, but he posted back-to-back months with an ERA over 6.00 in June and July. The 28-year-old has completed at least six innings in four straight outings, and he's walked more batters than he's struck out in just two of his first 13 starts.
The Cubs erupted for five runs against Reds starter Johnny Cueto on Saturday and tacked on another six against their bullpen. The Reds have gotten spectacular relief work from youngster Aroldis Chapman of late. The southpaw has posted a 1.40 ERA in his last 18 appearances.
"The main thing is, he's throwing strikes. He's throwing quality strikes," said Cincinnati manager Dusty Baker of his prized reliever. "We've got to pace him, his workload. He's doing great. He had that one period where he couldn't find the place, so he went down to Triple-A and Double-A and got it straight."
Reds: Chapman adjusting to life in the U.S.
With Chapman, it's more than stuff and location. Baker said that the 23-year-old -- a native of Holguin, Cuba -- is still acclimating to life in his new environment, an adjustment that trumps anything in baseball.
"A lot of his worry has been off-the-field stuff," said Baker. "He's trying to get stuff together. There have been a lot of adjustments he's had to make coming to this country. Part of it is being without his family.
"These guys have a life. They have ups, downs, problems like everybody else. The ones that can separate them and keep them separated for a few hours out here are the ones that perform the best."
Cubs: The hits, runs keep coming for Castro
Starlin Castro delivered two hits to add to his league-leading total on Saturday, but he did something else to grab the spotlight. Chicago's shortstop drove in four runs, the most since he plated six last season in his Major League debut. Castro has 148 hits this season, tops among all National Leaguers.
The 21-year-old is batting .314 and has scored 64 runs in his first 111 games, and he's weathered a slow month to maintain a productive season. He sizzled right out of the gate with a .348 batting average in April, then he simmered in May (.287) and June (.305) before drooping to .250 in July.
Chapman had a streak of 10 1/3 hitless innings snapped on Friday. That was the longest streak for a Cincinnati reliever since Chuck McElroy had 11 1/3 in 1994.
Arroyo hasn't won since June 25, but he's 4-0 with a 1.995 ERA lifetime at Wrigley Field.
Wells is 4-1 with a 2.96 career ERA against the Reds.
Cincinnati saw former first-round draftee Yonder Alonso hit his first career homer on Saturday.