Arlington (14-8) trailed 34-30 after three periods but outscored Mid-Vermont (16-6) 20-4 in the final quarter thanks to stellar free-throw shooting.
Senior guard Alex Hawley led the way, going 9-of-11 at the line in the fourth as he piled up a team-high 21 points.
As a team, the Eagles went 16-of-21 at the stripe.
Alex Trayah also tallied 14 points for Arlington. Austin Sayers led all scorers with 26 points for Mid-Vermont.
On Wednesday night, Arlington will head to the Final Four at the Barre Auditorium for the first time since 2007.
The Eagles await the winner of No. 3 United Christian and No. 6 West Rutland, who play tonight.
Raiders trip up BBA
MANCHESTER - Rutland broke free from a low-scoring first half to beat Burr and Burton Academy, 50-33, in girls basketball on Friday night.
Kaitlyn DeLong scored 13 of her game-high 24 points in the fourth quarter for the Raiders (12-8), who have won nine straight games. Rutland led 15-11 at halftime and 31-20 after three quarters.
Freshman Hannah Nicholson led BBA (10-10) with 18 points.
Arlington clips Wildcats
WILMINGTON - The Arlington Memorial High School girls basketball team likely clinched the sixth seed in the upcoming Division IV playoffs with a 47-36 win against Twin Valley on Friday night in both teams' regular season finale.
Molly Elwell led a balanced Arlington (11-8) attack with 15 points. Jennah and Julia Lacoste each added eight points. The Eagles led 26-12 at halftime.
"It was a hard-fought game. That team has gotten a lot better since the last time we played them," Arlington coach Larry Andrews said.
Hannah Swanson led the Wildcats with 10 points.