MILWAUKEE (Interstat) — The Chicago Cubs’ first-inning optimism evaporated in a torrent of Milwaukee Brewers offense as Jackson Chourio led a historic early onslaught before exiting with an injury in the Brewers’ 9-3 victory Saturday in Game 1 of their National League Division Series.

A sellout crowd of 42,678 at American Family Field watched the Brewers, the NL Central champions, batter Cubs starter Matthew Boyd and seize a commanding 1-0 lead in the best-of-five series.

The Cubs struck first and fast. On just the fifth pitch from Brewers ace Freddy Peralta, Michael Busch launched a solo home run to right-center field, momentarily silencing the home crowd and giving Chicago an early edge.

That lead was spectacularly short-lived. The Brewers sent 11 men to the plate in the bottom of the first, scoring six runs on six hits and capitalizing on a critical error. The inning began with back-to-back doubles from Chourio and Brice Turang, the latter driving in the first run. William Contreras followed with another double to tie the game.

After a groundout and a walk, Cubs second baseman Nico Hoerner misplayed a grounder from Sal Frelick, allowing Contreras to score the go-ahead run. Blake Perkins then singled home another, and after a walk reloaded the bases, Chourio delivered the biggest blow of the inning, a two-run single back up the middle that stretched the lead to 6-1.

The 20-year-old Chourio wasn’t done. In the second inning, he beat out a bases-loaded infield single to third, plating another run. It was his third hit and third RBI of the game, all recorded in the first two innings, making him the first player in postseason history to achieve that feat. The single gave Milwaukee a 9-1 lead, but Chourio immediately grabbed his right hamstring after crossing first base and was removed from the game.

His availability for the remainder of the series is in question, as he missed a month of the regular season with a strained right hamstring.

While the Brewers’ offense piled on, Peralta settled in after the first-inning homer. The right-hander, who finished the regular season with 18 wins, dominated over 5 2/3 innings, allowing two runs on four hits while striking out nine. The Cubs managed just one more run against him, a solo home run by Ian Happ in the sixth inning.

Boyd, the Cubs’ starter, was charged with the loss. He recorded only two outs while surrendering six runs, five earned, on five hits and two walks. The Brewers’ nine runs in the first two innings marked a franchise postseason record for runs in the first two frames of a playoff game.

After Boyd’s departure, the Cubs’ bullpen provided a measure of stability. Aaron Civale was instrumental in stopping the bleeding, delivering 4 1/3 scoreless innings of relief, allowing just three hits. Ben Brown followed with two more scoreless frames. Their efforts kept the game from becoming a complete blowout and saved the rest of the bullpen for the games ahead.

The Brewers’ relievers were equally effective. Aaron Ashby, Nick Mears and Jared Koenig combined for 3 1/3 innings of one-run ball, with Koenig surrendering a solo home run to Hoerner in the eighth inning to cap the scoring.

The Cubs, who finished the regular season with 94 wins, must now regroup quickly. They had won six of their final seven regular-season games and took three of four from the San Diego Padres to advance to this round, but were thoroughly outplayed in the series opener. The Brewers, who won 98 games, improved to 7-4 against the Cubs this season.

The loss defied pregame projections from Interstat, whose game simulator had projected a 6-4 Cubs victory. The total of 12 runs sailed over the pregame over/under line of 7.

The teams have a day off Sunday before resuming the series Monday in Milwaukee. The Cubs will need a victory in Game 2 to avoid returning to Chicago facing a nearly insurmountable 2-0 series deficit.