March Madness has begun and top teams are already heading home.

By Saturday night, two No. 1 seeds, Kansas and Purdue, No. 2 seed Arizona and No. 4 seed Virginia were all gone — and gone with them were millions of busted brackets.

Here is what to know, including the favorites and underdogs as well as key games to watch:

TOP SEEDS

The top four seeds in the tournament were given to Alabama, Houston, Kansas and Purdue. Each had its share of headaches to set up what is already proving to be a chaotic tournament. The Boilermakers were the first to fall, ousted in a first-round stunner, and the Jayhawks followed the very next day.

EAST REGION: The Boilermakers got a No. 1 seed for the fourth time, but Purdue was dumped by Fairleigh Dickinson in a near-historic upset. The region appears to be wide open for the likes of No. 2 seed Marquette, Kansas State, Tennessee, Michigan State and more. No. 5 seed Duke was ousted by the Volunteers. FDU or FAU will advance to the Sweet 16 in the bracket’s biggest underdog matchup.

SOUTH REGION: Alabama, led by coach Nate Oats in a challenging season, is a No. 1 seed for the first time behind SEC player of the year Brandon Miller, who has armed security on hand after being the subject of threats. The Crimson Tide opened the tourney with an easy win. Potential hurdles could include Baylor and Creighton. Princeton is heading to the Sweet 16 out of the South.

MIDWEST REGION: Houston got a top seed and won its opener before a rugged victory over Auburn even with All-American Marcus Sasser hobbled by a groin injury. Potential hurdles could include No. 2 seed Texas, No. 3 seed Xavier or the winner of a 4-5 matchup between Indiana and Miami.

WEST REGION: Kansas, the defending national champion that was without coach Bill Self in the tournament following a heart procedure, blew an 8-point halftime lead and lost to 8-seed Arkansas. Like the East, the West is now open for the likes of No. 2 seed UCLA, No. 3 Gonzaga and the winner of a juicy 4-5 matchup between UConn and Saint Mary’s.

SHINING MOMENTS

The unforgettable plays are piling up.

Princeton used a late run to earn its first NCAA Tournament win in 25 years by ousting No. 2 seed Arizona and then answered any skeptics by rolling Missouri to lock in its regional semifinal spot. Furman celebrated its first tourney appearance since 1980 with a win over No. 4 seed Virginia on a deep 3-pointer by JP Pegues with 2.4 seconds left.

Then came 16-seed Fairleigh Dickinson’s win over Purdue as the 22 1/2-point underdog stifled 7-4 center Zach Edey to advance and join UMBC in the record books.

All that happened before the Razorbacks and shirtless coach Eric Musselman celebrated their win over top-seeded Kansas.

GAMES TO WATCH

No. 16 seed Fairleigh Dickinson (21-15) vs. No. 9 seed FAU (32-3), Sunday, 7:45 p.m. ET (truTV)

One of these unheralded teams is going to the Sweet 16. The underdog Knights of FDU may be the smallest team in the tournament, but after knocking out All-America 7-foot-4 center Zack Edey and Purdue they will now face the ninth-seeded Owls. Florida Atlantic is coming off a thrilling win over Memphis and coach Penny Hardaway.

No. 6 seed Kentucky (22-11) vs. No. 3 seed Kansas State (24-9), Sunday, 2:40 p.m. ET, (CBS)

Wildcats abound! Oscar Tshiebwe pulled down 25 rebounds, the second-most in the tournament since 1973, as Kentucky beat Providence. That’s only four fewer rebounds than Kansas State grabbed in its 77-65 win over Montana State. K-State’s victory was its first in the tournament since 2018, when it beat ... Kentucky.

No. 7 seed Michigan State (20-12) vs. No. 2 seed Marquette (29-6), Sunday, 5:15 p.m. (CBS)

Quick, name two coaches you think are terrific. Tom Izzo and Shaka Smart need to be in your top 10, but only one will reach the Sweet 16 this tourney. The Spartans ousted Southern Cal behind 17 points from Joey Hauser, and will face a Marquette team to got 18 straight points from Kam Jones in the second half of a 78-61 victory against Vermont.

GO DEEPER

Gun violence has cost lives and disrupted college sports all season, touching some of the top programs in college basketball, including Alabama. Coaches have been thrust into uncertain and unwelcome roles in trying to navigate the topic — as well as the fallout from the Supreme Court decision to overturn Roe vs. Wade.

On a lighter note, if you feel you know March Madness pretty well, try this 25-question trivia quiz put together by AP.

PLAYERS TO WATCH

The NCAA Tournament is filled with great players and the AP All-America team is a good place to get familiar with the names. It’s also an event where guys you’ve never heard of can take a star turn. Guard play is always going to be important (see: Baylor, 2021 title winner) and there are some NBA prospects in the mix.

Bet on this, too: Some player — maybe more than one — will have a chance to join the mustachioed Doug Edert (remember Saint Peters’ inspiring run last year?) and find a way to cash in on their celebrity.

HOW TO WATCH

Every game of the men’s tournament will be aired — here is a schedule — either on CBS, TBS, TNT or TruTV and their digital platforms. CBS, which also has a handy schedule that includes announcing teams, will handle the Final Four and national title game this year.

The NCAA is streaming games via its March Madness Live option and CBS games are being streamed on Paramount+. Fans of longtime play-by-play announcer Jim Nantz should soak up every moment: It’s his final NCAA Tournament.

BETTING GUIDE

Who’s going to win the national championship? The betting favorites as of Saturday to reach the Final Four are (in order) Houston, Alabama, UCLA, Texas, UConn and Tennessee, according to FanDuel Sportsbook.