Gonzaga is the No. 1 overall seed in this year's NCAA men's basketball tournament after a dominant season that saw the Bulldogs go undefeated. Baylor, Illinois and Michigan were awarded the other No. 1 seeds by the selection committee on Sunday.

The Bulldogs are the fifth team to enter the NCAA tournament undefeated since Indiana's perfect season in 1975-76. They're also the first team to go wire-to-wire as the AP poll's No. 1 since unbeaten Kentucky in 2014-15.

The last teams to earn the 37 at-large bids -- one more than usual because the Ivy League canceled play this year -- were Drake and Wichita State, which play Thursday in a First Four game, and UCLA and Michigan State, two decorated programs with surprisingly low seeds that meet in another play-in game.

But four teams that didn't make it -- Louisville, Colorado State, St. Louis and Mississippi -- have been put on stand-by. They could find their way into the bracket if a team in the field notifies the NCAA by Tuesday night that it must withdraw because of health concerns. After that, if a team pulls out, its opponent will advance via what is essentially a forfeit.

The pandemic forced the cancellation of the tournament by the NCAA last year. This year, the entire field is heading to Indiana, which will host the whole tournament. Starting with the First Four, every game will be played in Indianapolis and surrounding areas. The first round will be played Friday and Saturday.

Gonzaga is the top seed in the West, a region that includes both Virginia and Kansas, two teams that had to withdraw from their conference tournaments because of COVID-19 issues.

Selection committee chair Mitch Barnhart said the committee was in frequent contact with leaders at Kansas and Virginia to ensure "the protocols were being met that would allow them to come to Indianapolis and participate.''

"We're confident at this point that we're moving forward to tip off Thursday with a full field of 68," Barnhart said.

Baylor had been on Gonzaga's heels all season, having lost just one game before dropping its second to Oklahoma State in the Big 12 tournament. The Bears are a No. 1 seed in the men's tournament for the first time in their history.

As the top seed in the South Region, Baylor could face either North Carolina or Wisconsin in the second round.

Illinois earned its No. 1 seed less than an hour after beating Ohio State in overtime to win the Big Ten championship. The Fighting Illini now have six wins over AP top-10 teams this season, tied for the most in a season in Big Ten history.

Illinois could face Loyola-Chicago in Round 2 in the Midwest Region. Loyola, which made a memorable Final Four run in 2018, is back in the NCAAs for a third straight tournament.

Syracuse is the No. 11 team in the Midwest, one of several bubble teams to get good news during the bracket reveal. Utah State is the No. 11 seed in the South.

Michigan narrowly missed having its highest regular-season winning percentage ever after a one-point loss to Ohio State in the Big Ten tournament to finish 20-4. The Wolverines are the top seed in the East; it's their first No. 1 seed in the NCAA tournament since 1993.

The Big Ten led all conferences with nine teams, followed by the ACC and Big 12 with seven each. It's the most Big Ten teams in a tournament in a single year ever, and tied for the third most by a single conference in a single season.

Fittingly for such an unpredictable season, some teams hoping to sneak in off the bubble were denied when Oregon State and Georgetown -- coached by former Hoyas superstar Patrick Ewing -- won their conference tournaments to steal bids they wouldn't otherwise have won.

"It's a different year. Different world,'' Ewing said. "The pandemic has definitely changed everything. I'm here quarantining in a room for 24 to 48 hours before we can get out and do things.''

Another unexpected entry is a familiar face: Rick Pitino. The coach, ousted at Louisville after a sordid recruiting scandal that enveloped the program for years, led his new team, Iona, from the ninth seed in the Metro Atlantic Athletic Conference tournament all the way to the league title and the automatic bid that comes with it. The Gaels, a No. 15 seed, will open Saturday against 2-seed Alabama.

Iona played only 13 regular-season games because of COVID-19 concerns that sidelined the Gaels for weeks. It was that kind of season.

Speaking of which, for the first time since 1976, both Duke and Kentucky will both be missing from the tournament. Like Virginia and Kansas, Duke pulled out of its conference tournament last week because of COVID-19, marking the end of a 13-11 season that never got on track.

ESPN's Stats and Information and The Associated Press contributed to this report.