GRAPEVINE, Texas, Dec. 1 (UPI) -- Five down, one to go.
The College Football Playoff selection committee on Tuesday unveiled its final preliminary ranking before it decides this weekend who will play for the 2015 national championship.
Tuesday's was the fifth ballot from the committee. The final ranking will come Sunday, determining which are the top four teams in the nation. Those teams will then participate in the sport's playoff bracket in January.
In evaluating the final week of the regular season for most teams, the panel left the top four unchanged: Clemson, Alabama, Oklahoma and Iowa.
Going into Tuesday, not many expected much difference in the top four -- but there were questions as to whether the order might be different from last week. Some analysts argued that either Alabama or Oklahoma, which each won convincingly Saturday, could ascend to the No. 1 spot this week.
Oklahoma (11-1, 8-1 Big XII) soundly defeated 11th-ranked Oklahoma State 58-23 to clinch the Big XII Conference championship, while Alabama (11-1, 7-1 SEC) beat Auburn 29-13 in the Iron Bowl. Meanwhile, top-ranked Clemson (12-0, 8-0 ACC) struggled in its victory over nine-loss South Carolina, the Southeastern Conference's worst team, and Iowa (12-0, 8-0 Big Ten) defeated Nebraska.
"The committee debated long and hard about the No. 1 and No. 2 teams," College Football Playoff committee chairman Jeff Long said.
As one of just two remaining undefeated teams, Clemson remained in the top spot Tuesday. Alabama stayed in second, Oklahoma in third, and the Tigers' fellow unbeaten, Iowa, in fourth.
Michigan State was ranked fifth, the first team out of the playoff field, and Ohio State climbed to No. 6. Notre Dame, sixth last week, fell to eighth after losing to Stanford.
The committee's final ballot will be decided after each conference crowns their champions this weekend.
The winner of the Iowa-Michigan State Big Ten championship will undoubtedly go to the playoff. Alabama will play No. 18 Florida for the SEC crown, Clemson will face No. 10 North Carolina in the ACC, and seventh-ranked Stanford will take on USC in the Pac 12.
Enough shakeup in the league title games could greatly alter the playoff landscape this weekend.
Stanford (10-2, 8-1 Pac 12) could sneak into the playoff if it wins the Pac 12 and either Clemson or Alabama loses. Ohio State, last year's champion, could also make a repeat appearance in the bracket if both the Tigers and Crimson Tide lose.
One of just five "Power 5" teams with only one loss so far, the Tar Heels remain a long shot for inclusion because they would need to climb six spots in one week. However, some commentators note, a resounding win over the top-ranked Clemson Tigers in the ACC championship game could possibly vault North Carolina into the top four.
The Big XII, shut out of the bracket last season, looks like it may be the very first conference in the playoff this time around. At No. 3, the Oklahoma Sooners don't risk losing this weekend because its league has no title game. And some analysts say a scenario that would push Oklahoma out of the top four is virtually nonexistent.
Title games for the ACC (Charlotte), Big Ten (Indianapolis), Pac 12 (Santa Clara, Calif.) and SEC (Atlanta) will be played Saturday. The selection committee will unveil its final ballot the following day, Dec. 6.
College Football Playoff Top 25 (Dec. 1):
1) Clemson 2) Alabama 3) Oklahoma 4) Iowa 5) Michigan State 6) Ohio State 7) Stanford 8) Notre Dame 9) Florida State 10) North Carolina 11) TCU 12) Baylor 13) Mississippi 14) Northwestern 15) Michigan 16) Oregon 17) Oklahoma State 18) Florida 19) Houston 20) Southern California 21) Louisiana State 22) Temple 23) Navy 24) Utah 25) Tennessee