The second-seeded Polar Bears (21-5) advance to the finals Saturday at 7:30 pm at Ursprung Gymnasium against No. 7-ranked and top-seeded Baldwin-Wallace, who edged fourth-seeded Wilmington 64-63 in the second semifinal game Friday night.
The third-seeded Muskies end their season with a 17-9 record.
Jared Bostelman, Ryan Lee and Kyle Gehle scored 12 points each for ONU.
Muskingum was led by Cole Pittis with 22 points, Brandon Todd with 13 points and Zach Ross and Jeremy Ady with 12 points each.
The ONU defense limited the Muskies to just 3-of-17 shooting from beyond the 3-point arc for 17.6 percent, while the Polar Bears nailed 10-of-22 of their three-point attempts for 45.5 percent.
Ohio Northern took a 38-29 lead into the halftime intermission. ONU used a 7-0 run to break a 14-14 deadlock and go up 21-14 with 10:06 left in the half.
A 6-0 run later in the half put the Bears up 34-25 with 2:13 to go in the period. Northern led 38-29 at halftime.
The Muskies trimmed the ONU lead to 53-46 with 11:06 left in the game, but the Polar Bears responded with an 8-0 run, keyed by three-pointers from Lee and Badenhop and capped by a bucket from Hostetler, to take a 61-46 advantage with 9:18 to play in the game.
Muskingum pulled within 66-60 with 3:14 left in the game on a pair of free throws by Ross.
But Hostetler would rally the Bears, scoring on the inside at 3:04 to make it 68-60. He then chased down a loose ball and fired a perfect pass to Lee for an easy layup and a 70-60 lead with 2:14 to go.
ONU would then make 9-of-10 from the foul line in the final 1:32 to ice the game.
"It seemed like we would get a big shot from someone when we needed it," ONu head coach Jeff Coleman said. "I'm very happy for our kids. We are in the finals and have a chance to win the league. Muskingum is a very good team. It makes it much better when you know you beat a very good team to advance.
"Jared Bostelman did a great job guarding Todd and that was a key. Bart Hostetler played a great game all night, too and made two big plays down the stretch. We had many players step up for us tonight."
Ohio Northern was 28-of-52 from the floor for 53.8 percent, while Muskingum made 25-of-59 of its field goal attempts for 42.4 percent.
Led by Hostetler's career-high 12 rebounds, ONU out-rebounded MC 36-25.