Timberwolves star Karl-Anthony Towns had to leave the game with 2:14 remaining after injuring himself on a dunk.
Towns scored only two of his 34 points in the final period -- and that was when he got free along the baseline for a dunk. After slamming the ball through, his momentum caused his body to fall horizontally and he appeared to land on his tailbone.
Minnesota lost for just the second time in nine games.
It was tied at 95 when Davis Bertans made a three-pointer to start a 12-3 run by the Wizards. Daniel Gafford added a dunk during that stretch, and Harrell capped the run with a dunk and a free throw. Neither team had led by more than eight before that three-point play made it 107-98 with 4:16 to go.
It was 112-107 in the final minute before Kentavious Caldwell-Pope made a three-pointer to close out the scoring.
Gafford had 18 points and 10 rebounds for the Wizards, who were back home after a four-game road trip.
Towns scored only three points in the first quarter, shooting 0-of-6 from the field. Then he scored 16 in the second and 13 in the third. Anthony Edwards had 25 points for the Timberwolves.
The Wizards outscored Minnesota 68-44 in the paint. Harrell shot 11-of-12 from the field and Gafford was 7-of-10.
Timberwolves: F Jarred Vanderbilt returned after missing Monday night's win over Indiana because of flu-like symptoms. F Jaden McDaniels missed a second consecutive game for the same reason. ... G Patrick Beverley (left adductor strain) missed his fourth straight game.
Wizards: G Aaron Holiday (non-COVID-19 illness) missed the game.
Timberwolves: Visit the Brooklyn Nets on Friday night.
Wizards: Host the Cleveland Cavaliers on Friday night.