A JaVale McGee masterclass has helped the Illawarra Hawks pull off the biggest upset of the NBL season with a comprehensive 107-93 victory over Melbourne United.

The bottom-ranked Hawks made surprisingly light work of top-ranked Melbourne at Wollongong's WIN Entertainment Centre on Wednesday night to claim six of the seven points on offer in the in-season Ignite Cup.

McGee racked up a season-best 37 points and 14 rebounds for the reigning champions in the Grand Final rematch, while shooting 13-of-21 from the floor and 10-of-11 from the free-throw line.

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Will Hickey added 18 points, while Tyler Harvey's 17 points included 4-of-5 three-pointers.

Finn Delany scored 21 points for United, Jesse Edwards had 19 points - including seven dunks - and Milton Doyle paired 16 points with 11 assists.

McGee was in everything as Illawarra steamed ahead 32-22 at quarter-time.

McGee clashed twice with Delany, before the Hawks giant exhorted the parochial home crowd by twirling his arm in the air late in the term.

Edwards, monstered early in his marquee match-up with McGee, threw down four second-quarter dunks but Illawarra's former NBA star otherwise continued to prove a problem.

McGee had 20 first-half points as the Hawks led 57-43 at the main break.

Critically, Illawarra went 18-of-19 from the free-throw line by the long break to Melbourne's 2-of-2 and comprehensively out-rebounded United 26-13.

Melbourne closed the gap to eight points but with Edwards forced to sit after chalking up his fourth foul and United's woes on the glass continuing, the Hawks still held sway 79-68 at three-quarter-time.

McGee drained his first three of the season midway through the fourth, which he followed with a wild celebration, as Illawarra's cushion swelled to 20 points.

Hickey and Melbourne's Fabijan Krslovic clashed after the full-time siren when the teams' post-game huddles overlapped midcourt. United were subsequently booed off the court with the Hawks' title defence suddenly looking less shaky.