Cleveland, Ohio - Celtics forward Grant Williams was the unwitting star of a viral moment as Cleveland Cavaliers pulled off an unlikely 118-114 OT comeback win in the NBA on Monday.

Boston, who led 92-78 at three-quarter time, and 102-91 with 4:30 remaining, gave up a 16-4 from that point to allow the Cavaliers to hit the lead with 24 seconds on the clock.

A Derrick White three-pointer put the Celtics back in front by two, before Donovan Mitchell tied things up at 109-109, but the visitors looked poised to get away with their sloppy fourth quarter after Williams was sent to the free throw line with 0.8 seconds left.

Audibly telling Mitchell "I'mma make both", the 24-year-old proceeded to miss the two attempts, blowing a golden opportunity and sending the game to overtime.

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The Celtics only mustered five points in the extra five minutes, clearly feeling the absence of missing star Jayson Tatum down the stretch, while Mitchell put the finishing touches on his 40-point night.

Cleveland's top scoring option finished 14-of-34 from the field, adding 11 rebounds and four assists, while rising second-year defensive ace Evan Mobley impressed with 25 points, 17 rebounds, and three blocks.

Jaylen Brown did his best to cover for Tatum, finishing with team-highs in points (32), rebounds (13), and assists (nine), and Malcolm Brogdon was strong off the bench with 24 points and five assists.

Boston (45-21) are now two games behind the Milwaukee Bucks in the hunt for the Eastern Conference's top seed, while the Cavaliers (41-26) are also trending towards having home court advantage in the first round, sitting fourth.