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Having beaten the Hawks by four points when they met in Wollongong on Friday, the Breakers repeated the dose in another arm-wrestle in Auckland on Sunday.
It ensures the Kiwis (15-9) will finish the regular season in the top four along with Melbourne United (17-7), Perth Wildcats (15-9) and Adelaide 36ers (15-10).
The Hawks were the only other team who could break into the post-season but a 10-14 record means they join Cairns, Brisbane and Sydney in planning for next year.
There are still two full rounds for the Breakers to fight for home court advantage in the play-offs, having been boosted by their first back-to-back win in a month.
As was the case on Friday, they unleashed a big finish after trailing the persistent Hawks entering the final quarter.
The hosts increased their defensive intensity and guard DJ Newbill found his range to finish with 20 points, supported by Shea Ili and Tom Abercrombie (17 each).
Tall Blacks guard Ili, 25, produced one of his more accomplished all-round displays, pulling off a key rebound in the dying seconds when Hawks opposite Mitchell Norton missed on a drive to the basket.
Guard Edgar Sosa subsequently sunk two clutch free throws with 3.5 seconds remaining to give the Breakers breathing space.
Rotnei Clarke unleashed a game-high 22 for Illawarra while Norton nabbed 14.
"They keep changing the rhythm of what they do defensively. We probably weren't as sharp in terms of execution but we finished shots better than we have done recently," Breakers coach Paul Henare said.
"From long range, DJ, Tom and Sosa put up some great numbers, and that helps."
The Breakers are away to league leaders Melbourne on Friday.