A day of drama has ended in a night of heartbreak for the NBL's Sydney Kings, who fell 90-88 to Melbourne United after a game-winning basket to Jack White in the final two seconds.

Hours after a failed medical assessment left Sydney to cut mid-season recruit and would-be NBL debutant Lamonte Turner, the Kings cried out for a point guard of the American's ilk against fast-starting United.

But after trailing by 20 points during Thursday's third quarter, the Kings closed to within six at the final change thanks to a 14-2 run inspired by Xavier Cooks (21 points, 10 rebounds) and Alex Toohey (10 points).

When Kouat Noi was fouled on the arc and went to the stripe for three shots, the NBL's comeback kings closed to within three points in the final 30 seconds and dared to dream.

United sharpshooter Chris Goulding then inexplicably turned the ball over with a lob up the court, paving the way for Izayah Le'Afa to shake off a forgettable night of shooting and land a triple that tied the game with four seconds left,

But from the inbound play, United's Matthew Dellavedova (11 points, eight assists) found White (23 points, 10 rebounds) under the basket for the former NBA forward to put up the game-winning lay-up behind a Goulding screen.

"Delly's an elite passer, obviously a player that can get Whitey open, get Chris open for a high-percentage shot in a short amount of time," said United coach Dean Vickerman.

"It was well-executed."

White, marking fellow elite forward Cooks, had his 11th double-double of the season.

"I think it's just understanding that for us to be at our best, I just need to be aggressive and assertive out there," he said.

The Kings were left to rue falling behind 32-16 at quarter-time, coming up with a staggering 11 turnovers in the first half to finish with 15 for that statistic.

"I thought we were sloppy with the ball, and lazy," coach Brian Goorjian said of the Kings' start.

Creativity was also a problem for the Kings as Melbourne built their crucial early lead. At halftime, Dellavedova (seven) had produced more assists than the entire Kings team (six).

The Kings missed a chance to move into second spot on the ladder - the cut-off for automatic qualification for the playoffs - and are at risk of falling behind ladder-leading Illawarra and United in second spot.

The Kings have not defeated either of those teams from a combined six meetings this season.

"The frustrating part is it's the same obstacle and we haven't overcome it yet," Goorjian said.

The match was Goorjian's 850th in the NBL across his time as player and coach, with 826 of those coming in the coaching hot seat.

"When (the milestone) came up, I definitely had a nice little reflection on how fortunate I am and all the good people that I've been around," said the six-time championship winner.

"I'm really blessed and really thankful, and really disappointed we lost tonight."