In his major league debut, highly touted Brewers prospect Jacob Misiorowski tossed five hitless innings before exiting with a leg cramp to pace Milwaukee to a 6-0 victory over the visiting St. Louis Cardinals on Thursday in the opener of a four-game series.

The hard-throwing 23-year-old right-hander struck out five before appearing to stumble on his third pitch of the sixth inning to Victor Scott II. Nick Mears relieved and finished the walk to Scott, the fourth charged to Misiorowski in an 81-pitch outing.

The Brewers announced later that Misiorowski left with right calf and quad cramping.

Misiorowski (1-0) topped 100 mph on four of his six pitches to Lars Nootbaar to open the game and fanned Pedro Pages on a 101.1 mph four-seam fastball to end the fifth.

Jackson Chourio hit a two-run homer to cap a five-run fifth against Sonny Gray (7-2) that put the Brewers up 6-0.

Gray, who was 4-0 in his previous six starts, allowed six runs on eight hits in 4 1/3 innings. He struck out four and walked one.

Isaac Collins walked to open the fifth but Gray picked him off first. Brice Turang and Caleb Durbin followed with consecutive singles and Joey Ortiz doubled in a run to make it 2-0.

Sal Frelick, who went 3-for-4 and scored twice, followed with a two-run single to left. Chourio then sent the first pitch from Gray 410 feet to center for his 12th homer.

The Cardinals did not get a hit until Willson Contreras’ leadoff single off Aaron Ashby in the seventh. Ashby covered the final three innings for his first save, allowing three hits with one strikeout.

The Brewers took a 1-0 lead in the second when Collins lined a two-out triple into the right field corner and Turang beat out an RBI infield single.

Misiorowski retired the first six hitters before walking Nolan Gorman to open the third. Gorman was then erased on a double play.

Misiorowski walked Nootbar to open the fourth and issued a two-out walk to Contreras, but got Alec Burleson on a popup to second.