All-Star guard Anthony Edwards and Donte DiVincenzo both exited in the first half, Edwards suffering a left knee injury when he came down awkwardly after contesting a basket shortly before half-time.
DiVincenzo was hurt less than two minutes into the contest and according to ESPN suffered a torn right Achilles tendon.
"This is for them," said Dosunmu, who made all five of his three-point attempts and became just the fourth bench player in playoff history to score 40 points in a game.
"Ayo was just out of this world," Timberwolves coach Chris Finch said. "Just play after play after play."
Trailing by four at half-time, Minnesota bore down in the second half to pull away in front of an ecstatic crowd at their Target Center arena in Minneapolis.
Naz Reid added 17 points off the bench to help the Timberwolves withstand a 30-point performance from Jamal Murray and a near triple-double of 24 points, 15 rebounds and nine assists from Nikola Jokic.
Three-time MVP Jokic and the Nuggets, who have lost three straight games, will be trying to fend off elimination in the best-of-seven Western Conference series when they host game five on Monday.
It promises to be tense after a scuffle at the buzzer sparked when Minnesota's Jaden McDaniels scored a basket with the outcome decided and most players heading to the sideline.
An irked Jokic rushed him and players had to be separated.