Las Vegas • The idea of an “NBA moment” — one big light bulb turning on for a rookie — might be mistaken. In reality, there’s a collection of such moments that cumulatively add up and make the NBA dream real for incoming players.

For Grayson Allen, one of those came Tuesday afternoon at Thomas & Mack Center, as his Jazz squad played against the Miami Heat, the treasured team of his youth. Coach Eric Spoelstra and team president Pat Riley watched from the baseline as the Heat ended up besting the Jazz 98-90 in Utah’s third and most scattered game in Las Vegas summer league so far.

Allen looked as he was finding a groove, scoring a team-high 17 points and adding three assists and five rebounds. The Jazz generally rest players as the summer league drags on; assistant Alex Jensen, who is coaching Utah in Vegas, said he wasn’t sure whether Allen had played his last game.

“It’s definitely cool,” Allen said. “It will be a little nicer in the regular season against real NBA teams.”

Allen, the No. 21 overall pick last month, looks ready for that level.

The 6-foot-5 guard showed his much-advertised yet not-as-often-seen rim-attacking ability against the Heat, including two dunks that rocked a somewhat sleepy Vegas crowd. There were also plays, such as a crosscourt pass to open up a corner 3-pointer, that showcased his increasing court awareness.

Within the organization, the Jazz have appreciated that Allen has shown the ability to play well on offense without the ball. Even though he took 17 shots on Tuesday, Allen has increasingly gotten looks off screens, on back cuts and other actions that will probably define his role in the NBA. He’s also been a willing and creative passer, which is something the Jazz anticipated.

“I think passing helps a lot, and I can shoot at the spot-up shots that I have in summer league,” Allen said. “During the regular season, if I come in for 10 minutes and can’t find a good shot, but can find a couple of assists, then that’s what I’ll do.”

In terms of his development, there also aren’t many surprises with Allen. He hasn’t shot for a high percentage (38 percent in Vegas), which is common for rookies. He also has lacked some defensive feel, which was a concern going into the draft.

Allen understands his shortcomings on defense, and he thinks continued integration into the Jazz scheme will hone his abilities there.

“Everything right now is, I guess, two steps late,” Allen said. “Once I get to practicing a lot, it will become instinctual: I see an action going on, I know my spot and recover back out. I think that will help.”

Summer league isn’t make-or-break for rookies, but in some cases, it gives validation. The Jazz have felt that with Allen, they’ve gotten the prospect they scouted. In the areas they thought he’d do well, he has. In the areas they thought he needed development, he does. Assuming he can keep pace with what Utah has projected for him development-wise, he could be a valuable addition to the rotation this season.

That’s still some ways away, however. It’s still becoming real to Allen, piece by piece. Another NBA moment? His first in-game dunk, after teasing his jams in pregame warmups for the last week.

“It was nice to get my first one,” Allen said. “I should have had like three before, but I didn’t have the legs to do it. But it felt good, especially early in the game.”

Jazz beaten by Heat

LThe quality of summer league play tends to melt down in the summer heat, and the Jazz are no exception.

Utah lost its second of its three games so far in Las Vegas, wilting in the second half to the Miami Heat, 98-90, on Tuesday afternoon.

Rookie Grayson Allen led with 17 points for the Jazz.

Utah was without big man Tony Bradley and without him, Miami second-year center Bam Adebayo got to the line against a feeble Jazz post defense, finishing with 24 points and nine rebounds (including 14 points off free throws). The Heat shot 30 free throws to Utah’s 12.

Diamond Stone, starting in place of Bradley, scored 17 points for the Jazz.