As the Jazz prepared to tip off, Nicole Mitchell was confused. Why was her son running onto the floor? He wasn’t a starter.

She counted the players. Five on the floor. No Rodney Hood. She started tearing up as she realized that her son, Donovan Mitchell, was about to make his NBA regular- season debut faster than anyone anticipated.

Even he didn’t know.

“Literally seconds before,” Donovan Mitchell said. “It was crazy. That’s when the nerves started to hit.”

As Hood went to the locker room with gastric distress, the No. 13 pick of the NBA draft made his first start unexpectedly. And it had some rocky moments in the blur of a first quarter which Mitchell said afterward he could hardly remember at all.

He wound up with 10 points on 3 for 11 shooting, four assists and three turnovers. But he also helped play point for the bench unit that ended up beating the Denver Nuggets in a 106-96 Jazz win, and his plus-22 mark helped show his defensive influence.

How would Mitchell grade himself? “About a C-minus.”

That might be in the same realm the coaching staff will have for their star rookie on Thursday morning when the tape comes out. Mitchell is still finding a role for the Jazz’s overall defensive scheme, and struggled at times when guarding Will Barton (23 points). He also made some iffy reads in pick-and-rolls and got two travels in quick succession.

“Tried to force things like I was back in Louisville [in college] and my shot got blocked about three times,” he said. “Just getting used to that. It’s not preseason. I learned that pretty quickly too.”

While the Jazz stop short of saying Mitchell’s growth is an urgent matter, there’s little doubt that he will play a large role this season after Dante Exum’s injury. He had a 26-minute debut, playing in Hood’s shoes, as well as Exum’s, and as well as Raul Neto who missed the game with a hamstring injury.

But it got better late. Mitchell assisted on Joe Johnson’s buzzer-beating 3-pointer at the end of the third quarter. After the Jazz took their first lead of the second half, Mitchell hit a jumper, then dished on back-to-back baskets to Alec Burks to push the edge up to 94-85.

Jazz coach Quin Snyder mentioned there were a few things he was eager to point out to Mitchell later on, such as when he took a long 2-pointer at the end of the half instead of either stepping out for a 3-pointer or driving to the basket. Some of those mental aspects need to be honed.

And yet the competitive energy Mitchell offered when he wasn’t expecting to start is something Snyder sees as a good foundation for his career.

“Donovan wasn’t prepared for that, but I think he was prepared to play,” he said. “Playing point guard in an NBA game when you haven’t done it before is not easy. I was pleased with Donovan’s readiness.”

As ready as he could be, anyway.