Melbourne United were left bitterly disappointed after dropping their third consecutive NBL game, this time to a South East Melbourne Phoenix outfit guided to victory by fast-finishing Derrick Walton.

Championship favourites to begin the season, United's 109-97 loss left them in the midst of their longest losing streak in two years, and cost them the chance to reclaim top spot on the ladder.

"Three (losses) in a row is just unacceptable," said ex-NBA guard Matthew Dellavedova.

"Everyone's pretty p***ed off, as we should be, and there's no one to blame except for ourselves.

"We're going to have to respond and we're going to have to hold each other accountable. Everyone's going to have to do their job and I'm confident that we'll be able to do that."

Second-placed United led by as many as 15 points at John Cain Arena on Sunday afternoon and scored 36 in their most prolific first quarter of the season.

But Melbourne conceded 9-0 and 14-0 runs in the second and third quarters, unable to contain Nathan Sobey nor match the size of Jordan Hunter (23 points, eight rebounds) without their own injured big man Marcus Lee.

Once Walton (14 points, seven assists) and a superb Sobey (22 points, seven assists, six steals) began to combine in the final quarter, the Phoenix closed in on victory.

Dean Vickerman felt poor defence and injuries to Lee and Chris Goulding worked against his side.

"We can't believe that it's the answer, bringing those guys back. Yes, it's going to help but we just have to be a lot better defensively," the United coach said.

"We're just not at a level defensively at the moment that can get us wins. We just can't stop people in the paint."

When Sunday's see-sawing match needed a hero in the final minutes, former NBA player Walton stepped up and shook off a wayward first half.

After United big man Rob Loe missed a free throw that could have tied the scores at 96, Walton marched upfield to extend the Phoenix's lead to four points with a three-pointer.

For his next magic trick, the American dished a pass through traffic to fellow recruit Sobey, who was fired up after his dunk.

By the time Walton drove through the paint for another two points, the Phoenix were up by eight points with fewer than 90 seconds remaining.

The win keeps the Phoenix in touch with the top six on the NBL ladder and ahead of the Adelaide 36ers and New Zealand Breakers to finish round 12.

"Every game is almost a do-or-die when you look at the ladder," said Phoenix coach Josh King.

"We needed this one tonight and I'm just really proud of the team effort, sticking together, especially being down 15.

"Happy for our guys and hopefully we can build on this."