ALVA, Okla (AP) -- Northwestern Oklahoma clinched its first trip to the NAIA championship game with a 21-6 win over the University of Mary (N.D.) Saturday.

A crowd of 2,000 watched the Rangers (12-0) win a defensive battle over Mary (11-2) that was played on a sopping-wet Ranger Field that was muddied by freezing showers.

Northwestern advances to the NAIA championship game Dec. 18 in Savannah, Tenn. The Rangers will play the winner of the game between defending champion Azusa Pacific (Calif.) and Georgetown, Ky.

Mary entered the game allowing 18.3 rushing yards per game, the least in NAIA. The Rangers were second, permitting 45 rushing yards a game. The Rangers ran for 247 yards, but threw for none. The Marauders threw for 86 yards, but ended with no rushing yards.

"We proved who had the best defense this time," said Northwestern coach Tim Albin. "We have an opportunity to go see who has the best team."

"The conditions were the worst I've seen," said Albin. "We put all the pressure on our defense. Our defense kept us in the ballgame."

The Rangers led 14-0 five minutes into the game with both scores coming with the wind at their backs. Mary took the wind in the second half, but managed only Verna Owen's 15-yard TD run 8:39 left in the third.

Northwestern earned 21 yards alone when Al Hunt kept his feet in the slop for a touchdown run. Then Charles McBride darted 58 yards for a TD, using Matt Walter's block.

The Rangers finished the Marauders on quarterback Preston Hartfield's 35-yard scoring run with 6:30 left in the game after Walter suckered the Maruaders into the middle. Walter, the offensive player of the game, ran for 111 yards on 24 carries before leaving with an apparent broken leg.

Northwestern grabbed four interceptions from U-Mary's Chris Schwab, three deep in Ranger territory. Issac Harvin nabbed two, including one at the Ranger 2-yard line. Shedrick Harris halted one Marauder drive with a pick at the 11, and Edwin Moore, the defensive MVP, cut a pass off at the 3.