The San Francisco 49ers have started off the 2019 season with a perfect 4-0 record. Despite that, they enter their Week 6 matchup with the Los Angeles Rams as slight underdogs.

Yes, you could argue the Rams are still 3-2 and they are the home team. However, it's still odd to see an undefeated team (one of just two left) as underdogs to a team just one game over .500.

With that in mind, the 49ers clearly need to have some players step up if they want to knock down their NFC West divisional rivals. Who exactly can do that though?

Here are two huge X-Factors for the 49ers in their Week 6 matchup with the Rams.

Running Game

Okay, this isn't just one player but a unit. I can't pick just one because San Francisco has had three running backs that have put in some great work this season.

Tevin Coleman has dealt with injuries, but he's back and looks fantastic. He has 120 yards and one touchdown on 22 carries (5.5 yards per carry) to this point.

Then there's Raheem Mostert. He has 236 yards on 41 carries (5.8 yards per carry) so far this season.

Finally, there's Matt Breida. Breida has 340 yards and one touchdown on 52 carries (6.5 yards per carry) so far.

Those three have all been absolutely phenomenal so far. If any combination of them can put together big games, San Francisco will be in a good spot.

To this point, the passing game hasn't been very good. Quarterback Jimmy Garoppolo is averaging 231.5 yards per game, including two games already with under 200 yards. He has also thrown four interceptions and has yet to hit the 300-yard mark in a game. Clearly, the offense is better when going through the running game.

That means the 49ers should focus on the run in this game. With three players proving to be very dangerous in that aspect, any one of them could be the difference maker against the Rams.

Therefore, it's not wise to call just one as the potential X-Factor. All three will likely get a chance to help the team, and all three have proven they can do so this year.

Nick Bosa

The 49ers defense has been absolutely superb so far this season. They've allowed the second fewest amount of passing yards per game at just 175.8. Meanwhile, they've allowed the fifth fewest amount of rushing yards per game at just 81.8.

That all equates to 257.4 total yards allowed per game, which is second best in the NFL. It's not like they're just keeping them from racking up yards either, San Francisco is keeping their opponents out of the end zone.

Their 14.3 points allowed per game is the fourth best in the NFL.

Clearly, something's working for San Francisco. Truthfully, it's every aspect. However, it's Nick Bosa that will play a major role in this game.

It appears the easiest way to stop the Los Angeles offense is to apply pressure on quarterback Jared Goff. When given pressure, he's not exactly calm and that's when he tends to struggle.

Bosa already has three sacks and a forced fumble in his rookie season. Two of those sacks and that forced fumble came in their Week 5 game against the Cleveland Browns.

If Bosa is starting to figure out the NFL, that's dangerous. He can become a menace weekly and if that happens against the Rams, the 49ers could definitely win this game.