Illawarra entered the fourth period on a 14-0 run inspired by import Darius Days (11 points, four rebounds) and looked primed to ride momentum to a series lead before a vocal crowd.
But with Dellavedova marshalling the perimeter in Iliโs absence, United kept the NBLโs best offensive team to only 10 fourth-quarter points.
The guard had missed his first five shots from the field but well and truly had his eye in when it counted at the death.
When Dellavedova landed a fadeaway shot with four minutes to play, United were back ahead, and edged further in front when he ducked around Kell for a lay-up in the paint.
Jack White gets physical for Melbourne United.Credit: Getty Images
Dellavedova was also key to unlocking Jack White, who had failed to put up a shot in Unitedโs game-two loss but was pivotal on Sunday.
White set the tone for Unitedโs 8-0 start by hitting a three-pointer only seconds after tip-off.
Ex-NBA forward White (20 points, five rebounds) went on to land two ally-oops from Dellavedovaโs game-playing in the third quarter and finished as the gameโs highest scorer.
โI think when Iโm having fun and Iโm not overthinking, I think that brings out the best in me,โ White said of his return to form.
โSimply put, I just wanted to enjoy the moment.โ
Kell slipped over and hurt his knee as he attempted to manoeuvre around Dellavedova with two minutes to play.
Dellavedova takes instruction from Melbourne United coach Dean Vickerman.Credit: Getty Images
The American was substituted out of the game and did not return, hobbling up the tunnel in clear frustration.
Tatum said they were โnot yetโ sure of the injuryโs severity.
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Kell was named in the All-NBL First Team for a brilliant first season at the Hawks and would be a significant loss as Illawarra fight to confirm a second championship banner.
United are feeling โpositiveโ about Iliโs hopes of returning from the latest in a string of concussions for Wednesdayโs game.
โItโs still questionable but heโs progressing the way weโd like right now,โ Vickerman said.
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