During a pre-season game prior to the 2018–19 season, Bortuzzo elbowed Washington Capitals defenceman Michal Kempný and was subsequently suspended for the remainder of the pre-season and one regular season game. Upon returning for the regular season, Bortuzzo suffered a lower-body injury in a game against the Toronto Maple Leafs on October 20. He was eventually taken off injured reserve on November 30, 2018. During a Blues practice on December 10, 2018, Bortuzzo fought teammate Zach Sanford. The two got a few punches in on one another before being separated by coaches. At the time, St. Louis had lost 8 of their last 11 games. On December 15, the Blues signed Bortuzzo to a three-year, $4. 125 million contract extension worth $1. 375 million per season through to the end of the 2021–22 season.