The unthinkable was happening to the top-seeded Grain Valley Eagles Thursday night in the 20th annual Sonic Showdown semifinal contest against Platte County.

The Eagles had routed the Pirates 66-39 earlier this season on Dec. 18, but the visitors held a 43-29 lead with 3:07 left in the third period.

Grain Valley used a 12-0 run to get back in the game, but had to settle for a great comeback that fell short as Platte County claimed a 56-55 victory on Deiondre Ragsdale’s free throw with 10 seconds left in the game.

After missing his first attempt, Ragsdale hit the second to make it 56-52. The Eagles hurried the ball down the court and got it to Ethan Macoubrie, who hit a long 3-pointer at the buzzer to account for the final score.

“We didn’t lose that game in the end, or in the second half,” Eagles coach Andy Herbert said after his team fell to 14-2. “We lost it in the first half. We didn’t even look like we wanted to play and Platte County came out and did a great job. We made that run at them, but we were never get over the mountain, over the hump, and get a lead in the second half and that’s frustrating.

“But if we’d have played like we are capable of in the first half, we wouldn’t have needed to make that run in the second.”

The Pirates led 16-9 after one period and 27-21 at halftime.

They padded their lead to 43-29 when the Eagles turned up the intensity. Four Pirate turnovers, two offensive fouls and a red-hot Eagles offense led by Josh Kilpatrick’s two 3-pointers, saw a 14-point deficit turn into a two-point deficit (43-41) going into the fourth quarter.

“We worked so hard to make it close, but we couldn’t get over that mountain top,” added guard Tate Collum, who led the Eagles with 19 points. “It’s frustrating because we know we’re a lot better team than we showed tonight.”

The Eagles, who shot just 4 of 22 from 3-point range and 20 of 59 overall, never managed to make it closer than 52-50 with 2:42 left in the game until the final basket.

Macoubrie added 14 points and 10 rebounds, Kilpatrick finished with 11 points and Andru Garrett had nine points and eight rebounds for the Eagles.

Ragsdale led the Pirates with 17 points.

The Eagles and Oak Grove will meet in the third-place game at 12:30 p.m. Saturday. Platte County will face Staley at 2 p.m. for the championship.

STALEY 54, OAK GROVE 35: Oak Grove simply couldn’t find a way to get past Staley’s strong defensive effort in the final game of the pool play side of the Sonic Showdown.

“I give all the credit to Staley,” Oak Grove coach Ty Hames said after his team fell to 11-3. “I’m disappointed we came out and seemed to forget about what we’d worked on in practice. This is a disappointing loss, but it’s one we can learn from.”

Jaxon Althaus led the Panthers with 17 points.

“Jaxon tried to carry us on his back, and he did for a while,” the coach added, “we just need to get more of the guys involved in the offense.”

Staley went 2-0 in pool play to advance to the championship, while Oak Grove finished 1-1.

PLEASANT HILL 68, VAN HORN 60: Terrion Seddens scored a team-high 16 points and Joell Wilson added 15, but it wasn’t enough for the Falcons to defeat Pleasant Hill in a consolation semifinal.

The Roosters’ Cale Ederer led all scorers with 26 points.

Van Horn is eliminated from the tournament while Pleasant Hill will meet Marshall at 11 a.m. Saturday in the consolation final.