You again, Alabama? It’s been long, Michigan? Good to see you, Georgia. This way to orientation, Cincinnati.

The College Football Playoff on Sunday announced those four schools — representing three conferences, 31 claimed national championships and plenty of hopes, hypes and expletives — as the field that would vie for this season’s title.

Left out without meaningful dispute: Clemson, Notre Dame, Ohio State and Oklahoma, among the bluest of blue bloods but programs that will be elsewhere on Jan. 10, when the championship game will be played in Indianapolis.

The playoff selection committee’s choices for the four-team tournament were widely expected after conference championship games on Friday and Saturday. Sunday’s rankings were responsible, though, for settling the matchups for the semifinal games on Dec. 31.

No. 1 Alabama will play No. 4 Cincinnati in the Cotton Bowl, and No. 2 Michigan will meet No. 3 Georgia in the Orange Bowl.

The Southeastern Conference again filled half the playoff field, and a rematch of its championship showdown, where Alabama defeated Georgia, is a prospect for the national title game. The Big Ten will be pleased, too, particularly about the opportunity to remind fans that Ohio State is not its lone power. And the American Athletic Conference, home to Cincinnati, will step into history as the first Group of 5 league to have a team appear in the playoff, which debuted with the 2014 season and replaced the Bowl Championship Series.

The Atlantic Coast Conference missed the playoff field for the first time, while the Pac-12 Conference failed to qualify a team for the fifth consecutive season. The Big 12 Conference, which started the weekend with Oklahoma State ranked fifth but then saw the Cowboys lose to Baylor in the league’s title game, will be absent for the second straight year.

Alabama, which, under Coach Nick Saban, has won six national championships since 2009, enters the playoff with the momentum of its most recent game as its finest of the season. Alabama (12-1) arrived at the SEC championship game as the playoff’s third-ranked team and opened that contest against Georgia, which was then No. 1, slowly. But Bryce Young, now a favorite to become Alabama’s second consecutive Heisman Trophy winner, ultimately threw for 421 yards and three touchdowns; he also rushed for one against a Georgia defense that had been better than any other in the Football Bowl Subdivision.

Alabama struggled in November, when it won three games by a touchdown or less, and it lost to Texas A&M in October. But Saturday’s demolition of Georgia’s perfect season, on top of 11 other wins, locked up a chance for the Tide to repeat as national champions. (Alabama routed Ohio State in last season’s title game.)

But Alabama may have some trouble ahead. Saban signaled on Saturday night that John Metchie III, who had 97 receiving yards on eight catches against Georgia before an injury late in the first half, would most likely miss the playoff.

“We have a couple other guys that may be injured,” Saban said. “It creates a lot of opportunity for a lot of other players. Hopefully, we’ll be able to get them to step up.”

Michigan (12-1) will make its inaugural playoff appearance after hounding Iowa, 42-3, in the Big Ten championship game. A week earlier, the Wolverines had downed Ohio State for the first time in a decade.

Indeed, much of Michigan’s most illustrious football history came in the first half of the 20th century, and the Wolverines have not claimed a national title since the 1997 season, before the B.C.S. and playoff were used to determine champions. But this year’s team has been far more ferocious than expected: The Wolverines did not make the cut in The Associated Press Top 25 preseason poll.

They wound up being a playoff lock.

The defense rising out of Ann Arbor deserves much of the credit. Aidan Hutchinson has seen his N.F.L. draft stock rise alongside his sack count: 13.5 this season, including three in the Ohio State game. David Ojabo, the Wolverine who is second in the Big Ten in sacks, has recorded 11.

Hassan Haskins picked up just 56 yards on 17 attempts against Iowa, but he also set Michigan’s record for rushing touchdowns in a single season, with 20.

“Nobody’s owed anything, nobody’s entitled to anything,” said Coach Jim Harbaugh, whose performance was under siege at the end of last season. But, he added, “When you’re around a group of guys that attack everything the way they attack their school work, their practice, and they want to give it their very best, you got a good feeling it’s going to happen.”

Georgia, the top-ranked team since the selection committee released its first rankings on Nov. 2, came into the weekend as the surest bet to make the playoff, where it last appeared in the 2017 season. Even falling to Alabama in such spectacular fashion was going to be nowhere near enough to let a season’s worth of work fall by the wayside.

Every other top-tier Power 5 team, after all, had at least one loss, too.

Like Michigan, Georgia can thank its defense, its unquestioned strength during its journey to 12-1. The thicket of defenders that includes Jordan Davis and Nakobe Dean has allowed an average of less than 10 points per game this season, a best in major college football. Georgia’s defense has given up about 254 yards each outing, less than any other SEC team.

The offense has shown flashes of dazzle — the tight end Brock Bowers, for example, had 139 receiving yards in the game against Alabama — but Georgia’s ambitions of advancing to the title game will most likely hinge on whether its defense can regain the form it had for almost the entire season.

Asked on Saturday how he might approach a potential rematch with Alabama, Coach Kirby Smart said he needed to review film from the game.

But, he said, “The first answer would be: Don’t leave people uncovered.” He added: “Let’s cover them, and then try to win some one-on-ones and get balls down. Because look, now, they’re going to throw and complete balls. They’re really good at doing that. At the end of the day, you have to put a body on a body and cover them. Some of the plays we gave were gifts.”

Cincinnati (13-0) experienced nowhere near as much heartburn on Saturday, when it beat Houston, 35-20, in the American’s league championship game. It had fixed a course for the playoff in October, when it went on the road and beat Notre Dame, 24-13.

The Bearcats have scored about 39 points per game and have averaged 429 yards of offense. The Cincinnati quarterback, Desmond Ridder, had a game this year that saw him throw three touchdown passes, run for a score catch a throw for another touchdown.

But the Cincinnati defense has been particularly sturdy and has allowed an average of 4 yards per play this season. Cincinnati’s opponents have scored a total of 25 touchdowns — the Bearcats have scored 70 — helping Cincinnati to lock down the conference lead for fewest points allowed per game (16.1).

In an interview this season, Luke Fickell, Cincinnati’s coach, had suggested that his team would not be distracted by playoff debates and whether their squad should, or should not, make the field as a Group of 5 program.

“You control your own destiny,” he said ahead of the Notre Dame game. “I mean, your destiny might not be going to the playoff if you win every game. But you control it.”

The Group of 5’s playoff berth, and the final rankings, came about six months after some college sports executives publicly floated a proposal to expand the playoff to a dozen teams. But divergent views on some details, like automatic qualifiers, have left negotiators without a consensus — and with diminishing confidence that the format will change before the 2026 season.

The N.C.A.A. has no role in the playoff, which is governed by the Power 5 and Group of 5 conferences along with Notre Dame. Although the playoff is already a money-printing machine for football’s most powerful conferences, media consultants believe that an expanded format would become the most lucrative event in college sports, outdistancing even the N.C.A.A.’s Division I men’s basketball tournament, a 67-game spectacle that brought in more than $850 million in television rights this year.