Cleveland State is headed to the NCAA tournament for the first time in 23 years, a surprising development that had to leave at least a few teams hoping to snag at-large bids on selection Sunday a bit dejected.

Cedric Jackson scored 19 points and Vikings used a flurry of 3-pointers to upset No. 16 Butler 57-54 in the Horizon League championship game in Indianapolis.

Also earning automatic bids Tuesday night were North Dakota State, which won the Summit League in its first season as a full-fledged member of Division I, and Western Kentucky as Sun Belt tournament champions.

Cleveland State’s last NCAA bid was 1986, when as a No. 14 seed the Vikings knocked off Bob Knight’s Indiana Hoosiers.

Against Butler on Tuesday night, Cleveland State (25-10) used six 3-pointers early in the second half to erase an eight-point lead by the Bulldogs (26-5).

Butler’s last lead was 48-47 midway through the period, then Jackson hit a 3-pointer and a floater in the lane to put the Vikings in front for good. Butler had two chances to tie in the closing seconds, but Shelvin Mack and Gordon Hayward missed 3-pointers.

Mack led Butler with 18 points and a career-high nine rebounds.

Cleveland State, which lost to Butler in the Horizon championship game last year and twice again to the Bulldogs this regular season, earned its first tourney title, giving it the conference’s automatic spot in the NCAAs field of 65.

Butler, ranked in the Top 25 most of the season, is expected to receive an at-large NCAA bid Sunday, and almost certainly would have been the only team from the Horizon to make the field.

Now the committee has two Horizon teams to accommodate, and one less at-large bid to hand out to teams such as Florida, Penn State and Arizona, with resumes that make their postseason hopes precarious going into their own conference tournaments.

At Sioux Falls, S.D., Ben Woodside made a 17-foot jumper from the top of the key with 3 seconds left to give top-seeded North Dakota State a 66-64 victory against Oakland.

‘‘I’ve been working on my offense for a while,’’ said coach Saul Phillips, who opted not to call a timeout and set up a play in the closing seconds. ‘‘It’s called ’get the ball to Woodside and get out of the way.’ It’s been effective.’’

NDSU (26-6), which won the regular-season title in its first season as a Summit League member, trailed most of the way and needed a rally in the final 5 minutes.

Woodside, the Summit League player of the year, finished with 17 points. He averaged 23 on the year, including a 60-point game against Stephen F. Austin in triple overtime.

He is one of five seniors who redshirted earlier in their careers as the Bison started to transition from Division II to I. They were targeting this season, hoping to take one good shot at an NCAA tournament bid.

Their patience paid off.

Michael Tveidt had 21 points for North Dakota State and was 4-for-4 on 3-point shots. His last 3 came with 1:26 left, put NDSU ahead 64-62 and capped an eight-point run.

Oakland’s Keith Benson responded with a dunk for a 64-all tie with 12 seconds to play. Rather than call timeout, NDSU charged down court and gave Woodside the ball.

At Hot Springs, Ark., A.J. Slaughter scored 18 points, and Western Kentucky beat South Alabama 64-56 to win the Sun Belt tournament and earn its 21st NCAA tournament berth.

The Hilltoppers (24-8) wasted a 15-point first-half lead and trailed 43-39 in the second. Slaughter put Western Kentucky back ahead 44-43 with a 3-pointer, part of a decisive 14-3 run.

The Hilltoppers reached the NCAA round of 16 last year and provided one of the tournament’s most spectacular plays when Ty Rogers sank a desperation 3-pointer over three defenders to beat Drake in the first round.

DeAndre’ Coleman led South Alabama (20-13) with 27 points.