Michael Busch greeted Paul Skenes with the fourth leadoff home run of his career and the Chicago Cubs moved to the brink of their first playoff berth in five years with a 4-1 victory over the Pittsburgh Pirates on Tuesday night.

The Cubs winnowed their magic number to one by chasing Skenes (10-10) during a rare rocky outing for the NL Cy Young Award favorite. Busch led off with his 29th homer of the season, a shot to the final row of seats above the Clemente Wall in right field, and finished with three hits as Chicago won for the sixth time in seven games.

Nico Hoerner added three hits and Carson Kelly, Dansby Swanson and Mosies Ballesteros had two apiece for the Cubs in support of starter Cade Horton (11-4), who bolstered his NL Rookie of the Year credentials by limiting the Pirates to one run over five innings. The 24-year-old right-hander is 8-1 with a 0.92 ERA since the All-Star break.

Brad Keller worked a perfect ninth for his fourth save.

Skenes is a near lock to become the first pitcher to win Rookie of the Year and follow it up by capturing a Cy Young the next season since former New York Mets star Dwight Gooden in 1984 and 1985. Yet the 23-year-old's final start at PNC Park this season was a rare misstep at a place where he has dominated.

The towering right-hander gave up three runs on seven hits with three walks and six strikeouts and was pulled after 3 2/3 innings, the shortest start of his career outside of a brief two-inning stint at Yankee Stadium last fall in an appearance that was mostly ceremonial at the end of his breakout rookie season.

The last-place Pirates have dropped 10 of 11.

Busch's 385-foot shot on the game's fourth pitch was a sign of things to come. Pete Crow-Armstrong singled home Ian Happ later in the first, just the second and third runs Skenes has allowed in the opening inning all season.

Skenes has 209 strikeouts, one short of Mitch Keller's single-season record for most by a right-handed pitcher in the franchise's 137-year history.

The NL Central rivals meet for the final time this season on Wednesday when Chicago's Matthew Boyd (13-8, 3.05 ERA) starts against Johan Oviedo (2-0, 2.81).

Cubs chase Cy Young favorite Paul Skenes, move to cusp of playoff berth with win over Pirates