Heading into Week 4 of the 2015 season, seven teams were undefeated.
One of those teams (the Cardinals) lost that week. Another (the Panthers) didn't stop winning until Week 16.
Ultimately, of course, Arizona and Carolina outlasted everyone in the NFC to meet in the conference title game. So a team's ability to hold off that first loss of the season doesn't necessarily reveal much about its long-term prospects.
That said, I thought it would be interesting to examine the five undefeated teams remaining this season and project which squad will stay undefeated the longest:
1) New England Patriots
How did we get here? The Patriots just keep coming up aces, no matter how many backup quarterbacks they need to lean on. Bill Belichick and the coaching staff -- including offensive line coach Dante Scarnecchia, this offseason -- know how to make it work using smoke and mirrors. Still, signal callers Jimmy Garoppolo and Jacoby Brissett are both pretty good; New England likely won't have to worry about finding someone to take the reins whenever it's time to move on from Tom Brady.
How long will it last? is pivotal. Rex Ryan's Bills can be dangerous, especially . But presuming the Patriots can get past the Bills, they'll get Brady back from his four-game suspension against the Browns and should be able to roll from there. Pittsburgh will be a tough place to play and the Seahawks present an obvious challenge , but at this point, we can feel confident in New England's coaching edge. I think the Pats have a good chance to leave their  with a 14-0 mark.
2) Denver Broncos
How did we get here? First-time starter Trevor Siemian is providing better quarterback production, statistically speaking, than Peyton Manning and Brock Osweiler did last season. But I wonder what will happen as opponents accumulate more tape on Siemian -- will he start to struggle as defenses learn more about him? A lot of credit goes to coordinator Wade Phillips and the Von Miller-led defense, which hasn't skipped a beat after losing Danny Trevathan and Malik Jackson to free agency. Much depends on how long and if Shane Ray can help keep teams from keying on Miller. Ray's effort Sunday (three sacks ) was a great start.
How long will it last? The Buccaneers are an immediate threat , but Denver is good against the pass and Tampa will be . Visiting San Diego will be a challenge -- it always is -- but I can see the Broncos reaching their Week 11 bye with a 10-0 record. Sooner or later, of course, someone will get to this squad, and I think the Chiefs have a good shot to upset the apple cart in Denver . Even if the Broncos clear that hurdle, they'll likely fall to the Pats .
3) Minnesota Vikings
How did we get here? for Sam Bradford was sensational. I've been a fan of his since his sophomore year at Oklahoma, and while I still worry about his injury history, he's really playing well, improbably helping the Vikings make up for the loss of three key players in Teddy Bridgewater, Adrian Peterson and Matt Kalil. Head coach Mike Zimmer is a standout coach, the perfect personality for this team, while Norv Turner is a great offensive coordinator. Oh, and then there's the principal driving force behind the perfect start: an utterly loaded defense.
How long will it last? Hosting the Giants will be tough . That said, the Vikings' new stadium is going to be a very unfriendly venue for visiting teams, thanks to the crowd noise. I like them to beat New York in Minnesota, hand the Eagles their first loss and ultimately get to 9-0. But then in (vs. the Cardinals), the streak should run into serious trouble, as Arizona matches up very well with the Vikings. If Minnesota escapes that showdown, the Cowboys could end the party .
4) Philadelphia Eagles
How did we get here? This is an interesting team. Front-office honcho Howie Roseman did a great job turning this ship around. I thought Carson Wentz would be good, but he has far exceeded my expectations. I've been surprised by the poise he's shown, especially coming from a small school; he's the front-runner for Offensive Rookie of the Year, without question. I think he's going to be a special quarterback, though I do wonder, as I do with Siemian, what will happen as opponents begin to gather more tape on Wentz. New defensive coordinator Jim Schwartz's unit has been a big boost so far.
How long will it last? The Eagles should be 5-0 heading into with the Vikings, but asking Wentz to beat that defense is a tall order -- Zimmer feasts on young quarterbacks. Thus, I think 5-0 is the best we can expect in terms of perfection from the Eagles. Should Philadelphia somehow hold off Minnesota, trips to play the Cowboys and the Giants provide opportunities to stumble. Things get really gnarly in Weeks 11 () and 12 ().
5) Baltimore Ravens
How did we get here? This team is tough to figure out. Adding Eric Weddle and returning Terrell Suggs to the defense seems to have done wonders for that unit, which is the NFL's second best through Week 3. But quarterback Joe Flacco is not having a knockout season after recovering from a torn ACL, sitting on a 77.4 passer rating and a 3:4 touchdown-to-interception ratio. John Harbaugh's coaching staff is an obvious boon, as is the fact that C.J. Mosely is playing like he did in 2014, for Defensive Rookie of the Year honors. Justin Tucker's accurate leg (9-of-9 on field-goal tries) has been key. But the opponents they've beaten thus far this season have a combined record of 1-8.
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