The upset belonged to the host Lady Trojans, who knocked off Blue Eye in straight sets to start the evening.
Steve Voyak's girls controlled the tempo and were the more aggressive team in claiming the 25-16, 25-18 win over the Lady Bulldogs.
Southwest never trailed in the first set and led by as many as 11 points in claiming that set, 25-16. The Southwest front line of Taylor Mettlach, Shannon Mitchell and Montana Hendrix dominated the Lady Bulldogs and forced them into a passive bump return game.
After trailing 13-9, Blue Eye came alive and fought back to take a 15-13 lead in the second set. Southwest scored the next five points to take a 18-15 lead.
The Lady Trojans led 20-17 when freshman Jaime Shrum's service run carried Southwest to match point. Blue Eye's last chance service opportunity failed, and the Lady Trojans claimed the set and the match.
Southwest advance to play top-seeded Ash Grove. The Lady Pirates received a bye in the opening round.
The Clever Lady Blue Jays also enjoyed a straight set victory, knocking out Crane, 25-12, 25-18.
Clever advanced to play Marionville, a winner in three sets over Purdy in the final contest of the night.
Marionville, with an advantage in height and experience, seemed destined to make short work of Purdy, but the Lady Eagles shook off an early 3-0 deficit and played even with the Lady Comets.
Purdy seized every available opportunity to take an improbable 25-23 win in the opening set.
But then the Lady Comets eliminated the costly unforced errors and took full advantage of their height at the net.
Amy Hicks used all of her 73 inches to stuff Purdy's front line for three of Marionville's first 10 points in the second set, leading her team to a 10-7 lead. Freshman Kyrah Reavis's serve led to nine straight points as Allison Schatz went on a scoring spree, and the lead blossomed to 19-7.
Purdy fought to stay alive in the set but could not find an answer for the net play of the Lady Comets. Marionville took that set 25-10 to tie the match.
In the decisive third set, Marionville swept to a 14-3 lead and never led by less than 10 points the rest of the way.