Watch: Celtics' Grant Williams misses two game-winning free throws

The Cavaliers went on to win in overtime, the third time this season they beat the Celtics in extra time. This came one day after the Celtics lost to the New York Knicks in double overtime. Two days, three extra periods, two losses.

Williams made four of five 3-pointers in the game, but he couldn't hit his only two free throws of the contest. It must have especially stung when Cleveland's Donovan Mitchell spoke to Williams before the keys shots, and Williams said, "I'm gonna make both."

Mitchell finished with 40 points, but his most devastating play may have been whatever he said to rattle Williams. 

Cleveland stayed a game ahead of the Knicks for fourth place in the Eastern Conference, while Boston fell to a game and a half behind Milwaukee for the top spot. Boston also fell to 4-7 in overtime for the season, the losing record solely due to their 0-3 overtime record against Cleveland.

Meanwhile, Cleveland is a perfect 7-0 in overtime games this year, thanks to Mitchell's 36 points in the extra periods. That's second in the league to Boston's Jaylen Brown, who has 43 points, albeit in three more games and 15 more minutes.

One key to Mitchell's success? He's perfect on his free throws in overtime. Ironically, so is Williams. It's the regulation freebies that have been a problem.