Jansen started at designated hitter and went 2-for-3 with a walk in Sunday's 8-2 loss to the Yankees.
Jansen, who was acquired from the Blue Jays on Saturday, made his debut for Boston. The catcher served as the DH and gives the Red Sox a needed right-handed bat that can harm lefties, against whom Jansen has a .718 OPS this season. He replaced Reese McGuire (.533 OPS against lefties), who was designated for assignment, as the Red Sox's backup to catcher Connor Wong.