Top draft pick Cooper Flagg has become the first 18-year-old to score 40 points in an NBA game, but his efforts weren't enough to prevent Dallas falling to a 140-133 loss against Utah.

Flagg, who turns 19 on Sunday, passed his previous personal best of 34 points with a hook shot over the top of Ace Bailey in the fourth quarter before reaching 40 with a free throw in the final seconds of regulation time.

With a pair of foul shots in overtime on Tuesday (AEDT), the former Duke Blue Devil had the equal-highest scoring game for any Mavericks rookie in the franchise's 46-year history.

"Obviously we didn't win. So it's tough for me to want to be happy, or any of that, but obviously it's a success," said Flagg, who had a bag of ice on his ankle after rolling it at the end of regulation.

Flagg showcased his scoring prowess from mid-range, while a pull-up three-pointer was another highlight that caught the Jazz defence napping just before the half.

But the Mavericks were left to rue an 11-0 run from the Jazz in the final quarter that left them scrambling to tie the game with two Max Christie free throws in the final seconds.

In overtime, the Jazz kicked clear thanks to Lauri Markkanen (33 points, 16 rebounds) and Kyle Filipowski (25 points, nine rebounds).

Flagg finished with 42 points to go with seven rebounds and six assists to confirm excellent signs for the NBA's most recent No.1 draft pick.

"The more time he spends on the floor, the more he sees, the better he gets. He displayed it all tonight," Dallas coach Jason Kidd said.

Flagg has been playing his best basketball the past few weeks and has averaged 25.7 points in the last seven games. He's also playing aggressive enough to get to the line and went 15 for 20 against Utah.

"It's come a long way from the start of the season, so I'm proud of that fourth quarter," Flagg said. "It's a new game ... but I am getting more and more comfortable ... and just settling in, honestly, just being myself and letting the game come to me."

PJ Washington was also full of praise for the rookie.

"We were going to Coop. He was killing them the whole game, so they finally tried to double him," Washington said. "It doesn't surprise me at all. I know exactly what he's capable of. He's a special player so there will be a lot more to come."

The Miami Heat are on the NBA's longest active losing streak after a 106-96 loss to the Toronto Raptors made it five defeats on the trot.

The Raptors snapped their own four-game losing streak as Brandon Ingram scored 28 points to help the visitors come from behind in Miami.

The Heat had led for the majority of the first three quarters, at one stage by 11 points, before the Raptors' 17-2 run swung the game in the final term.

Making matters worse for the Heat, Nikola Jovic suffered an elbow injury when he fell on a drive to the basket only 12 seconds after entering the game.

The Detroit Pistons extended their lead atop the eastern conference standings with a 112-105 defeat of fellow heavyweights Boston Celtics.

Cade Cunningham put up a double-double with 32 points and 10 rebounds to help Detroit exact revenge on the Celtics, who ended their franchise record-equalling 13-game winning streak last month.

The Pistons are now on a four-game run.

Australian big man Jock Landale had eight points from the bench as the Memphis Grizzlies romped to a 121-103 victory over the LA Clippers.