 Happ had a very strong 2018 season with the Yankees with ERA of 2.69.Despite a shaky 2019, he finished strong with ERA under 2 for the month of September,

On October 4, 2019, Happ made his first appearance as a reliever for the Yankees, pitching in the eighth inning against the Minnesota Twins in American League Divisional Series.He was initially slated to be a long reliever because CC Sabathia was not included in the 25-man roster for that round.