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ALL season Illawarra's depth has been much vaunted but never was that more on show than tonight as it forced the NBL Championship Series into a deciding Grand Final Game 5 on Sunday, Will Hickey leading the Hawks to a gutsy, brave and ultimately soaring 80-71 Game 4 win in Melbourne.

In what was a tough watch early, United contained Illawarra to its lowest half of the season when it led 32-28 at the main interval. But the Hawks responded by holding Melbourne to 71 for the game, United's lowest score of the season.

The Hawks went into the match without import playmaker Trey Kell (knee), United still down Shea Ili (concussion protocols) but Illawarra was dealt a second serious blow in its quest to level the best-of-five series at 2-2 when it lost star centreman Sam Froling to a right Achilles issue.

He came down hard under the Hawks' basket, endeavoured to run it off but instead had to sub out, his night and his series done.

Playing just 8:38, Froling already accumulated five points, four rebounds and two assists at a time Illawarra was reeling in the second quarter and could ill-afford to lose him.

Coach Justin Tatum started Hickey in place of Kell and gave the power forward start to Darius Days who he arguably underplayed in Sunday's Game 3 home loss.

Out to an early 15-5 buffer on a Hyunjung Lee three, the Hawks were looking focused early, Chris Goulding missing his first seven shots, copping a justified flop warning, Ian Clark also wayward and Marcus Lee with two quick fouls.

It was Matthew Dellavedova (17 points, 7 rebounds, 6 assists) who finally had the scoreboard ticking over for Melbourne with a three and a fadeaway before Flynn Cameron cut the deficit to 12-15 at the end of a dour first quarter.

Delly's 3-pointer immediately tied it when the second quarter started and when Clark (16 points, 0-of-5 threes) added a floater, Melbourne was 17-15 ahead on a 12-0 run.

Lachy Olbrich (13 points, 6 rebounds, 3 assists) finally had the Hawks underway but with Dellavedova en route to 13 first-half points, Melbourne looked more comfortable than the 32-28 halftime scoreline suggested.

Tatum showed no reluctance to try multiple players and different rotations, Hickey (career-high 22 points, 6 rebounds, 8 assists, three steals) stepping up and Mason Peatling (7 points, 5 rebounds, two steals and a block) providing far more energy and effort than his numbers suggested as Illawarra seized the third quarter 23-16.

Haste makes waste and had been the story of the Hawks' last quarter fadeouts but this time, despite Goulding (17 points, 4-of-9 threes) nailing some customary impossible shots, it was a 29-23 period of smart basketball that included some wonderful play by Hickey and back-breaking triples from Tyler Harvey and Days.

Todd Blanchfield and Dan Grida also provided bench energy and Wani Swaka Lo Buluk was active as the Hawks sent the series back to Wollongong for its monumental conclusion on Sunday.

NBL CHAMPIONSHIP SERIES SCHEDULE (Best-of-Five Grand Finals)

ILLAWARRA HAWKS v MELBOURNE UNITED

Game 1: Melbourne United 96 (Dellavedova 18, Goulding 15, Lee 14, Ili, Lee 15 rebs; Clark, Goulding, Ili 4 assts) d Illawarra Hawks 88 (Froling 16, Hickey 14, Blanchfield 13, Swaka Lo Buluk 11; Hickey, Froling 7 rebs; Hickey 8 assts) at WIN Entertainment Centre, Wollongong. Crowd: 5,491 Melbourne leads series 1-0

Game 2: Illawarra Hawks 102 (Harvey 24, Froling 23, Kell 18, Swaka Lo Buluk 12; Kell 8 rebs; Kell 6 assts) d Melbourne United 100 (Clark 31, Goulding 17, Dellavedova 14, Krebs 12; White, Lee 6 rebs; Lee, Dellavedova 5 assts) at John Cain Arena, Melbourne. Crowd: 9,135 Series tied 1-1

Game 3: Melbourne United 83 (White 20, Dellavedova, Clark 16, Goulding 14; Lee 8 rebs; Dellavedova 11 assts) d Illawarra Hawks 77 (Hickey 12, Days 11, Swaka Lo Buluk, Kell 10; Kell 8 rebs; Kell 3 assts) at WIN Entertainment Centre, Wollongong. Crowd: 5,512. Melbourne leads series 2-1

Game 4: Illawarra Hawks 80 (Hickey 22, Olbrich 13, Harvey 12; Days 11 rebs; Hickey 8 assts) d Melbourne United 71 (Dellavedova, Goulding 17, Clark16; Dellavedova 7 rebs; dellavedova 6 asst) at John Cain Arena, Crowd: 10,175 Series tied 2-2

Game 5: Sunday, March 23, WIN Entertainment Centre, Wollongong, 2:30pm AEDT