Lyndsay Harris led the defending Class 1-A state champions with 18 points in a 69-56 victory.
It was a solid team effort for the Lady Eagles after senior and leading scorer Kayle Addison hit the floor with a severely sprained left ankle with 1:57 remaining in the first period. Addison did not return to the game and emerged from the training room with an ice bag wrapped on her injured ankle.
The untimely exit slowed St. Stephen's for a bit, but they emerged behind 18 points from Lyndsay Harris and a 22-point third period to advance to semifinal action via a 69-56 win.
St. Stephen's led 14-8 when Addison fell and Rock River took advantage of the confusion to build a 28-16 lead before the Eagles recovered.
A buzzer-beating 3-pointer by Rock River's Lydia Moore gave the second-seeded Longhorns a 19-14 lead after one period.
St. Stephen's roared back on the play of Angel Redman, who tallied 10 points on a variety of moves in the paint in the opening half, along with timely baskets from Trinity Goggles and Harris and an opportune 3-pointer from Josette Oldman.
An old-fashioned 3-point play behind a layup and following free throw by Goggles and a free throw by Whisper SunRhodes tied the game at 31-31 at intermission.
Rock River took their final lead of the game on an Andi Todd 3-pointer to open the third, but it was all Eagles after that.
Martina Brown hit a jump shot, Harris drained a 3-pointer, followed by scores off offensive rebounds by Goggles and Harris and the Eagles fought to a 45-39 lead.
Another Harris three and a buzzer-beating layup by SunRhodes gave the Eagles a 12-point cushion with one period remaining.
St. Stephen's saved the best for almost last, when Goggles tossed the ball from half court to a posted-up Harris on the low block.The ball arched through the Events Center air, found Harris wide open and she scored on the play with 30 seconds remaining.
Harris' 18 points led the Eagles, while Goggles added 14 and Angel Redman 12.
Rock River's points came primarily from Todd with 23 and Moore with 24.
St. Stephen's 14 17 22 16 - 69
Rock River 19 12 10 15 - 56
St. Stephen's - Trinity Goggles 6 2-4 14, Kayle Addison 2 0-0 4, Martina Brown 3 0-0 6, Josette Oldman (1) 0-0 3, Angel Redman 6 0-0 12, Whisper SunRhodes 3 2-3 8, Cassie Lawson 1 0-0 2, Orelia Lawson 1 0-0 2, Lyndsay Harris 4 (3) 1-2 18. Totals 26 (4) 5-11 69
Rock River - Taylor Broyles 1 (1) 0-2 5, Andi Todd 3 (3) 8-10 23, Michelle Bunce 2 0-0 4, Lydia Moore 7 (1) 7-11 24. Totals 13 (5) 15-25 56