ARIZONA (5-0, 2-0 Pac-12)
How they got here: Arizona is 5-0 for the first time since 1998 with a young offensive backfield featuring redshirt freshman quarterback Anu Solomon and true freshman running back Nick Wilson. Linebacker Scooby Wright leads a defense that has eight sacks over its last two games. In its last two games, Arizona edged California 49-45 on a Hail Mary and pulled off a 31-24 stunner at No. 12 Oregon, which was ranked second at the time.
Potential roadblocks: Arizona has a tough home test with Southern California on Saturday and has three more games with ranked teams: Nov. 1 at No. 18 UCLA, Nov. 22 at No. 24 Utah and Nov. 28 at home against No. 20 Arizona State. If the Wildcats stay unbeaten through the regular season, they'd still have to survive the Pac-12 championship game.
GEORGIA TECH (5-0, 2-0 ACC)
How they got here: The Yellow Jackets have found an ideal quarterback for Paul Johnson's triple-option attack in Justin Thomas, who has rushed for 470 yards while also throwing seven touchdown passes with only one interception. Georgia Tech beat Georgia Southern 42-38 on a touchdown with 23 seconds left and erased a 10-point deficit in a 27-24 triumph over Virginia Tech. "I'd say they're resilient," Johnson said. "Nothing much seems to affect them. We get behind and nothing changes. They don't panic."
Potential roadblocks: Georgia Tech hosts defending ACC Coastal Division champion Duke on Saturday and closes the regular season with a Nov. 15 home game against Clemson and a Nov. 29 trip to No. 13 Georgia. The Yellow Jackets avoid No. 1 Florida State in the regular season but could face the Seminoles in the ACC championship game if both get that far.
MARSHALL (5-0, 1-0 Conference USA)
How they got here: Marshall's the one team on the list that isn't really a surprise. Before the season, Marshall was touted as a team that could go unbeaten thanks to star quarterback Rakeem Cato and a tissue-soft schedule. Cato directs an offense that leads all FBS teams with 595.6 yards per game. "Cato has done a tremendous job," Marshall coach Doc Holliday said. "He is extremely unselfish and could care less about his stats. What he cares about is winning the football game."
Potential roadblocks: Marshall has a potentially tricky home game Saturday with Middle Tennessee, which beat the Thundering Herd 51-49 last season. The only other remaining opponent that currently owns a winning record is UAB, which hosts the Herd on Nov. 22. Marshall also could end up in the Conference USA championship game.
MISSISSIPPI STATE (5-0, 2-0 SEC)
How they got here: Quarterback Dak Prescott has emerged as a Heisman Trophy candidate while leading Mississippi State to its highest ranking ever. The Bulldogs have gained at least 500 yards in each of their games this season, though their brutal schedule gives them little time to celebrate. "The difference between a pat on the back and a kick in the rear end is about six inches," Mississippi State coach Dan Mullen said. "We have to make sure we keep in the high-end of those six inches right there because if not, it will turn to the second."
Potential roadblocks: Mississippi State hosts No. 2 Auburn on Saturday. The Bulldogs also have two upcoming road games against Top 25 teams: Nov. 15 at No. 7 Alabama and Nov. 29 at No. 3 Ole Miss. If the Bulldogs get through that grind unscathed, they'd still need to play the SEC championship game.
TCU (4-0, 1-0 Big 12)
How they got here: The Horned Frogs already have matched their win total from last season, when they finished 4-8. TCU's offense is averaging 516.2 yards per game, 171.4 more than last season. That represents the best statistical improvement of any FBS offense this season. "We are good enough to win the Big 12," TCU linebacker Paul Dawson said after a 37-33 victory over No. 11 Oklahoma, which was ranked fourth at the time.
Potential roadblocks: TCU visits No. 5 Baylor on Saturday and hosts No. 16 Oklahoma State on Oct. 18 and No. 17 Kansas State on Nov. 8.
Imagine a playoff that includes Arizona facing TCU in one semifinal and Mississippi State meeting Georgia Tech in the other.
Is it a long shot? Sure. But it's not quite as far-fetched as it may have seemed before this season of surprises began.
No. 3 Mississippi State, No. 9 TCU, No. 10 Arizona and No. 22 Georgia Tech are all unbeaten after starting the season unranked. The list of undefeated teams that opened the season outside the Top 25 also includes Marshall, which remains unranked despite winning its first five games by an average margin of 31.8 points.
"It's way too early, but I thought before the season when everybody started lining teams up for the four-team playoff, I said, you know, there's so much that can happen in the regular season in college football," Arizona coach Rich Rodriguez said. "All the polls are nice for the fans, but they're going to be presumptuous. Let's wait and see what happens because I think the 'Power 5' conferences have so much more parity than they've ever had that there's so much more that's still going to happen over these next six or seven weeks."
Here's a look at these five unbeaten teams that started the season unranked.