University made 8-172 in its semi-final against the hosts at Sutherlands Park, but Gosnells hit back, chasing down the target with one ball to spare and three wickets in hand.
Earlier in the day, Aaron Keverne-Onyon blasted 49 from 27 balls while Chris Prescott took four wickets as Gosnells won its quarter-final against Perth by 19 runs.
Ashton Agar smashed 54 from 39 balls, while Ian Bell was cleared and made 49 from 39 balls as Uni edged Willetton in its quarter-final.
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READ NOWAshton Turner took three wickets and top scored with 33 as Fremantle defeated Claremont-Nedlands by five wickets at Iluka Sports Complex.
Claremont-Nedlands only managed 6-130 with James Allenby top scoring with 40, before Freo chased down the target in 19 overs.
Perth Scorchers big hitter Mitch Marsh could only manage 15 from 22 balls, while Englishman Tom Abell blasted an undefeated 32 off 23 balls.
Fremantle knocked out hosts Joondalup in their morning quarter-final with Scorchers pair Sam Whiteman (50 from 24) and Mitch Marsh (55 from 32) dominant.
Claremont-Nedlands defeated Bayswater-Morley by eight wickets led by Nick Hobson (68n.o.) and Chris Brabazon (47n.o.).