Utah (36-36) used a 10-0 run to open the fourth quarter and led by as many as 19 while outscoring Phoenix 56-32 in the paint.
Jefferson finished 12 of 23 with nine rebounds, two blocks and two steals.
Jefferson had 27 points combined in the previous two games, but picked up his game with Wednesday's injury to second-year backup Enes Kanter, who dislocated his left shoulder early in the second quarter. Kanter will have an MRI Thursday and could miss a couple weeks of action.
"I cannot feel any pain right now," Kanter said after the game. "I couldn't open my arm, I looked over my shoulder, and I was like, 'Oh my.' That was the first time [this has happened], so I was like, 'Ow.'"
Wesley Johnson had 22 points and Luis Scola 20 to lead the Suns (23-49), who dropped their fourth straight.
Utah shot 52 percent.
With Phoenix out of the playoff picture, the Suns chose to rest starting guard Goran Dragic.
Utah led by as many as 13 points in the third quarter. But the Suns were within 75-71 going into the fourth thanks to Johnson's 10-point third, including a 3-pointer at the buzzer.
Utah opened the fourth just as it started the game, with hot shooting and a take-it-to-them attitude.
Jefferson scored on a layup, converted a three-point play and hit a midrange jumper to open the fourth and Alec Burks added a 3-pointer during the run as the Jazz stretched their lead to 85-71 with 8:58 left.
The Jazz led by as many as 13 in the second quarter and 53-44 at halftime.
Utah opened 6 of 6 to take a 12-6 lead and shot 70 percent (16 of 23) in the first quarter.
Scola tried to keep the Suns in it, hitting four of his first five shots and 7 of 9 in the half to lead all scorers at the break with 15.
But the Suns were outscored 22-4 in the paint in the first half.
Phoenix started rookie Kendall Marshall in place of Dragic, who was coming off a season-high 31-point, 12-assist effort in a 102-100 loss to Brooklyn on Sunday.
While the Jazz won their second straight, they lost a key piece.
Kanter left the court in obvious pain with 10:23 left in the second quarter with what team officials said was a dislocated left shoulder. He is to have an MRI on Thursday morning.
Kanter was biting hard into his mouthpiece, supporting his left arm and stopped courtside as if he wanted to try to pop the joint back into place. Team trainer Gary Briggs led him to the locker room shortly thereafter.
The injury occurred while the 6-foot-11, 248-pound Kanter was diving for a loose ball and collided with Suns center Hamed Haddadi, who is listed at 7-2, 265 pounds.
Kanter is averaging 7.3 points and 4.4 rebounds for Utah while playing with the second unit.
Utah next plays at Portland Friday night.