Liz Tolley leveled 13 kills and Camilla Foresti had 11 as the Polson Pirates beat Corvallis in four sets 25-17, 20-25, 25-24, 25-22.
The Pirates will face Havre at 6 p.m. on Friday in the undefeated semifinal.
Foresti also had 15 digs for Polson.
HAVRE 3, BILLINGS CENTRAL 1
The third-seeded Havre Blue Ponies delivered the biggest upset of the State A tournament so far.
Havre overcame a one-set deficit to win three straight matches as the Blue Ponies stunned Billings Central 17-25, 25-20, 26-24, 25-20 in the second round on Thursday evening.
The Blue Ponies trailed 7-0 in the fourth set before rallying back to tie the set up at 16-16.
Havre now advances to the undefeated semifinal tomorrow while the Rams fall into a loser-out match.
First Round Matches
Billings Central 3, Dillon 0
The defending Class A champions are one step closer to a repeat title.
Mya Hansen and Zi'onna Keikam-Morton each had seven kills as the Billings Central Rams swept past Dillon 26-24, 25-11, 25-20 in the opening round of the State A Volleyball Tournament on Thursday morning at Brick Breeden Fieldhouse.
Maddie Yochum added six kills for the Rams, and Leikam-Morton had five aces. Hansen and Alaina Woods each had three blocks for Central.
Dillon was led by a match-high 12 kills from Ainsley Shipman and three blocks apiece from Kylie Konen and Zoey Morast.
The Beavers fall into a loser-out match against Hamilton at 8 a.m. Friday. Central plays a semifinal match today at 6 p.m. against Havre.
HAVRE 3, RONAN 0
Avery Carlson, Yelena Miller and Jade Wendland each supplied six kills as the Blue Ponies overcame an early first-set deficit to cruise past the Maidens 25-16, 25-17, 25-14 to setup a semifinal match against the Rams.
Ronan falls into a loser-out game tomorrow at noon.
CORVALLIS 3, HARDIN 0
Madeline Gilder racked up 22 kills and had 15 digs to lead the Blue Devils to a 25-19, 25-18, 25-15 sweep of the Bulldogs. Hailey Anderson had three aces for Corvallis and Tahnee Lewis provided 19 assists.
POLSON 3, MILES CITY 0
The Pirates swept through the Cowgirls 25-11, 25-23, 25-19 to setup a second-round match against Corvallis. Miles City fell into a 10 a.m. Friday loser-out match against Hardin.
MILES CITY 3, HAMILTON 1
Bailey Nowicki leveled nine kills as the Cowgirls topped the Broncs 25-16, 25-19, 23-25, 25-23 in an early-morning game at Shroyer Gymnasium. Miles City will face top-seeded Polson at 4 p.m.