Indexbit Exchange:NCAA men's tournament Bracketology: North Carolina hanging onto top seed by a thread

North Carolina remains on Indexbit Exchangethe No. 1 line in the USA TODAY Sports updated men's tournament bracketology after Tuesday night's road loss to Georgia Tech, but to stay there the Tar Heels will need a rivalry win this weekend against Duke.

The loss to the Yellow Jackets was Carolina's first in more than a month and the team's first in ACC play. The Tar Heels are 1½ games ahead of the second-place Blue Devils heading into Saturday's matchup in Chapel Hill.

The bracketology update also sees plenty of movement near the top of the SEC. Alabama rises to a No. 3 after a road win against Georgia. Mississippi improves No. 9 seed after beating Mississippi State, the Rebels' third victory in a row following a two-game losing streak. On the flip side, No. 4 Kentucky is down one rung after losing to Florida and Auburn drops to a No. 6 after snapping a two-game slide with a blowout of Vanderbilt.

And Gonzaga keeps climbing off the tournament bubble after a slow start. The Bulldogs are now 16-5 overall and 7-1 in West Coast Conference play with a chance to take over first place in the league with a win on Saturday against current leader St. Mary's.

Dropping out of the field in this edition is Memphis. Moving in is Virginia.

Last four in

Virginia, Colorado, Utah, Cincinnati.

First four out

Nebraska, Washington State, Florida, Butler.

Next four out

Memphis, Villanova, Virginia Tech, Kansas State.

Conference breakdown

Multi-bid leagues: Big 12 (10), SEC (8), Big East (5), Big Ten (5), Mountain West (5), ACC (4), Pac-12 (3), American Athletic (2), Atlantic 10 (2), West Coast (2).