The freefalling Cubs committed five errors, including two in a seven-run seventh inning, in a 9-2 defeat to the Pittsburgh Pirates on Tuesday night.
Chicago dropped to 82-75 and would be eliminated with one more loss or Milwaukee win. The Cubs have not missed the playoffs since 2014.
Aided by a fielding error by second baseman Ben Zobrist and errant throw by reliever Danny Hultzen, the Pirates sent 13 batters to the plate in the seventh as they chased starter Kyle Hendricks and erased a 1-0 deficit. Pittsburgh stopped a nine-game losing streak in which it had been outscored 87-26.
Hendricks didn't allow any hits until the sixth.
The first five batters had hits in the big inning and the sixth reached on Zobrist's error. Colin Moran's RBI single tied the score, Kevin Kramer hit a two-run double for a 3-1 lead and two runs scored when Zobrist couldn't handle Erik Gonzalez's hard grounder for an error.
Hultzen threw wide of second base in attempting to get a forceout, and Adam Frazier capped the outburst with a run-scoring double.
Hendricks (11-10) allowed six runs - five earned - and six hits in six-plus innings.
Kyle Schwarber hit two doubles for Chicago and rookie shortstop Nico Hoerner drove in both runs with a double in the fourth inning and a single in the eighth. Hoerner also made the first two errors of his young career.
Francisco Liriano (5-3) pitched a perfect seventh. Pittsburgh rookie Mitch Keller gave up one run and seven hits in five innings.
Chicago stranded 11 runners and went 1 for 10 with runners in scoring position.
Jon Lester (13-10, 4.51 ERA) will start Wednesday night. He is 3-1 with a 4.51 ERA in his last five outings.
Dario Agrazal (4-5, 5.08) is 0-2 with a 7.43 ERA in his previous three starts.