NBA round-up: Mitchell hits game-winning shot as Cavaliers remain perfect
The Bucks looked poised to claim their second win of the season after a 41-point performance from Damian Lillard (34), who gave his side a 113-112 lead after draining a jumper with 10 seconds left on the clock.
But Mitchell expertly ran the final few seconds down before nervelessly sinking the final bucket to leave Milwaukee's Fiserv Forum in stunned silence.
There was still time for one last attempted buzzer-beater from Lillard, but the Bucks' star's effort bounced off the backboard to leave Cleveland sitting pretty with a perfect 7-0 record on top of the Eastern Conference.
Mitchell, who finished with 30 points, four assists and three rebounds, credited his game-winning shot to a possession-securing rebound by team-mate Isaac Okoro moments before.
"It's not about the shot - it's about Isaac Okoro's rebound," Mitchell said. "That's what it's all about. I did my job, Isaac did his job, we all did our jobs.
"That's a big win. They played their behinds off. As a group, we just continue to fight and claw."
The all-around performance saw six Cavaliers players make double figures in a see-saw clash that included 19 lead changes.
Sam Merrill caught the eye with 17 points off the bench for Cleveland, raining in five three-pointers while Jarrett Allen had 15 points with 12 rebounds.
The Bucks were left pondering another uneven performance which has left them one place off the bottom of the Eastern Conference with a 1-5 record.
Lillard, who scored just four points in a blowout defeat to the Memphis Grizzlies on Thursday, bounced back in scintillating fashion, shooting 10-of-15 from outside the arc for the Bucks.
"I've been in the league 13 years and I've had my share of rough nights, ups and downs, individually and as a team," Lillard said.
"The only way to go from there is back to work and keep your mind right and try not to think about it too much."
Giannis Antetokounmpo also impressed in Milwaukee's losing effort, finishing with 34 points and 16 rebounds.
