All you needed to do to turn a healthy profit through three weeks this NFL season is bet underdogs.

That's it. Close your eyes, bet every single NFL underdog, profit.

Underdogs had another big Sunday. Favorites were just 4-9-1 against the spread in Sunday's games. To this point in the season, underdogs are 27-18-2 against the spread, according to Covers.com. That's 60 percent.

If you can find a betting trend that's as easy as "bet NFL underdogs" and it hits 60 percent, you've done very well for yourself.

Underdogs had a big Week 3

Week 3 started with the favored Cleveland Browns covering against the Pittsburgh Steelers. Then Sunday kicked off and the dogs took over.

The only favorites to cover on Sunday were the Baltimore Ravens, Cincinnati Bengals, Philadelphia Eagles and Los Angeles Rams.

Eight underdogs not only covered but won straight up. It would have been nine-for-nine if the Detroit Lions didn't blow a lead in the final minute to the Minnesota Vikings. The Lions didn't trail until 45 seconds remained in the game.

The other underdogs all won straight up. What a day for underdog moneyline bettors.

The biggest underdogs to win straight up were the Indianapolis Colts and Miami Dolphins, though the Jacksonville Jaguars were technically the biggest if you bet them when they were 7-point underdogs, before that line dove to +3 on Friday. The Colts closed at +4.5 after briefly being +7 during the week. They beat the Kansas City Chiefs in the last minute. The Dolphins closed at +4.5 against the Buffalo Bills as well, after being as high as +6 during the week. They held on to a 21-19 win.

There were some sweats, especially on the moneyline, but the underdogs came through. They have been for three weeks.

Why are underdogs covering?

There are swings in NFL trends over a season. Oddsmakers adjust to teams and other trends quickly and they usually even out over time.

Still, there's a good reason underdogs are covering, and it should be somewhat reliable in this season or any NFL season.

The NFL wants parity and every season we get closer to every team being .500 going into the final week. The Miami Dolphins and Philadelphia Eagles were the only 3-0 teams left after Sunday (the New York Giants can improve to 3-0 on Monday night). There was one 0-3 team: the Las Vegas Raiders. It's the first time since 1959, when the NFL had 12 teams, that there is only one 0-3 team, according to ESPN Stats and Info.

If 85-90 percent of the league is somewhere between 2-1 and 1-2 — there isn't as big of a gap between the 25th-best team in the NFL and the fifth as you think — taking the points seems like the right play. Or just skip the points and take the moneyline on those underdogs.

If it seems like a crazy start to the season, it has been. The odds will adjust to it. But don't expect this season's underdog trend to go away.