The Timberwolves had the game seemingly wrapped up — ahead by eight with 50 seconds left to play.
But a comedy of errors and missed free throws caused them to lose to the Suns 114-113.
Collin Gillespie hit the winning shot for Phoenix with 6.4 seconds to play, and Julius Randle missed a potential winning three for the Wolves.
With the loss, the Wolves (10-6) remain winless against teams above .500 this season. The Wolves fell to 2-1 in NBA Cup play and will need a win over Oklahoma City on Wednesday to have a chance of advancing to the quarterfinals.
“We lost our minds. Poor execution. Turnovers obviously and didn’t stay locked in for the last 90 seconds,” Wolves coach Chris Finch told reporters in Phoenix.
Phoenix (10-6) made its last-second push without Devin Booker, who had fouled out (16 points).
The Wolves lost despite 41 points from Anthony Edwards, who missed a pair of free throws that could have put the Wolves up three with 12.7 seconds left. Edwards also had a key turnover on an inbound pass with 45.9 seconds to play that led to a three from Jordan Goodwin. They cut the Wolves’ eight-point lead to three in a matter of six seconds.