CMU, the No. 5 seed, earned its third win over the rival Broncos in a season for the first time in program history.
"It's hard to beat a team three times in a row. It's hard to beat a team twice in one season but three times in a row is really hard regardless of their record," Austin said. "When you play a rival, all records go out the window. You just have to be ready to play at all times."
Although the Broncos entered Tuesday's game as the No. 12 seed, CMU head coach Keno Davis knew his team was in for a battle.
"Much like the rest of the conference, we knew no game in the postseason would be easy. I'm proud of our guys to be able to continue to battle all season long. Tonight's game was a good sample of what we've seen all year; guys playing extremely hard, winning on toughness determination and (the ability to) keep battling."
HOW IT HAPPENED
Possessing a two-point lead at halftime, CMU exploded to start the second half. Layups from Austin and Kevin McKay and a David DiLeo 3-pointer forced Western Michigan to call a timeout to stem the tide with the Chippewas in front 42-33.
Leading by 10 points with 13:21 left, CMU went on another 7-0 run, featuring a pair of free throws and a layup from Austin and another 3-ball from DiLeo, giving the Chippewas a 60-43 advantage.
WMU responded with an 11-5 run to pull within 11 points with 6:12 left to play but could not cut further into CMU's lead for the rest of the game, ending its 2018-19 campaign with an 8-24 record.
Austin lead the Chippewas, finishing one assist shy of a triple-double. He posted 24 points and 13 rebounds for his eighth double-double of the season. Austin's nine assists came against just one turnover. He also tallied four steals, adding to his single-season record.
Roundtree contributed 20 points on 50 percent shooting (4-of-8) from beyond the arc with six assists and five rebounds. David DiLeo had 14 points, shooting 4-of-7 from 3-point range.
WMU senior center Seth Dugan finished with 29 points and 17 rebounds.
The Chippewas will square off with No. 4 seed Kent State in quarterfinal action at approximately 2 p.m. Thursday at Quicken Loans Arena in Cleveland. CMU defeated the Golden Flashes, 84-74, in McGuirk Arena on Feb. 19.