The San Francisco 49ers are off to a perfect start in 2019. No, seriously, a perfect start. Through five weeks, they're 4-0.

If there is any knock on the team, it's been their competition. So far they've played the Tampa Bay Buccaneers (2-3), Cincinnati Bengals (0-5), Pittsburgh Steelers (1-4) and the Cleveland Browns (2-3).

Due to that, some are questioning whether or not the 49ers are a serious threat. Especially considering how tough their NFC West division is. Despite a 4-0 record, they find themselves barely ahead of the Seattle Seahawks.

Seattle has a 4-1 record, and the Los Angeles Rams are 3-2. Don't expect those teams to go anywhere either.

So why should you consider the 49ers legitimate playoff contenders? Here are three reasons why.

3. They're 4-0

Jimmy Garoppolo, George Kittle, 49ers, Browns
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Let's start with the absurdly obvious reason the 49ers are legitimate playoff contenders. They're 4-0. San Francisco is already in a very comfortable spot.

The 49ers are one of just two undefeated teams left in the NFL (the New England Patriots are 5-0). They're the only NFC team that's still undefeated too.

While that doesn't lock up anything this early, it definitely makes things a lot easier.

Even if they just go .500 for the rest of the year (6-6), San Francisco would end the season with a 10-6 record. That's definitely good enough to be in the conversation of a postseason spot.

While they do have a tough remaining schedule, it's also important to remember that they have some easier games as well.

San Francisco still has the Arizona Cardinals (currently 1-3-1) on their schedule twice. They also get a game against the completely lost Washington Redskins (currently 0-5). Therefore, while it's easy to point at the schedule the 49ers have already had, it's not like all the “easy” games are out of the way already.

4-0 doesn't guarantee anything (other than at least four wins), but it's a damn good start. Any team that's still undefeated this late into the season is a serious contender for a playoff spot.

2. Defense

That entire defense is fantastic. This much is highlighted by the numbers.

So far, the 49ers have allowed the second fewest total yards (257.5) per game. They are second in passing yards per game (175.8) and fifth in rushing yards per game (81.8). So it's not like they're really good against one part of the game but struggle with the other.

Meanwhile, the 14.3 points per game that San Francisco allows is the fourth fewest in the NFL. Clearly, this whole defense thing is working out well for them.

It will be hard for them to be this dominant all year. Especially considering the teams they still have to face. The Los Angeles Rams twice, the Seattle Seahawks twice and the New Orleans Saints and Green Bay Packers should all cause problems.

That being said, San Francisco has shown they are absolutely for real defensively. While they might not be as dominant against those teams, they won't be steamrolled on defense either.

This defense should be able to keep the 49ers in games each week and help pull out a few extra victories as well.

1. Matt Breida and the Running Game

Tevin Coleman, Matt Breida, 49ers
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The entire running game of the 49ers has been superb in 2019. However, Matt Breida deserved his own special shoutout.

Tevin Coleman has 120 yards and one touchdown on 22 carries (5.5 yards per carry). Meanwhile, Raheem Mostert has 236 yards on 41 carries (5.8 yards per carry). Finally, Breida has 340 yards and a touchdown on 52 carries (6.2 yards per carry).

Do you see the trend? If you don't I'll let you in on the secret. They're all having ridiculous years. Mostert is on pace for 944 yards and Coleman is on pace for 960 yards (he's only played in two games so far due to injury). Then there's Breida, who is on pace for 1,360 yards.

To be fair, it's unlikely all three of them will keep up this ridiculous production. However, the fact that through four games the 49ers have three running backs putting up these types of numbers is absurd.

It takes all the pressure off quarterback Jimmy Garoppolo and it will keep their legs fresh. Being able to lean this heavily on the running game will also help San Francisco control the clock.

Win the time of possession battle and you'll win a lot of games.