Max Strus scored his fifth 3-pointer of the game, a 59-footer, to secure a 121-119 victory over the Dallas Mavericks.
Strus's shot was the second-longest game-winning buzzer-beater in NBA history, measuring 59 feet.
The Cavaliers improved to 12-3 since January 26 with Mitchell scoring 31, Strus contributing 21, and Allen contributing 19.
Luka Doncic, who played for the Mavericks, recorded 45 points and 14 assists.
Kyrie Irving contributed thirty points for Dallas, which fell for the second time in ten games.
Doncic's 11th triple-double was completed with nine more points.
The Cavaliers took a 56-41 lead in the second quarter, but Doncic took over after a timeout for Dallas.
Irving received standing ovations during player introductions and was honored with a video during a first-quarter timeout.