The Kansas City Chiefs (5-0) face another tough test as they travel to face the dynasty that is the New England Patriots (3-2) Sunday night at Gillette Stadium in Foxborough, Massachusetts.

The Patriots' success over the past 18 years under head coach Bill Belichick has been well-documented—17-straight winning seasons, 12 AFC title games, eight Super Bowl appearances and five Super Bowl titles.

They are the personification of success, and they currently find themselves standing on the tracks of the freight train that has been the start of the Chiefs' 2018 season, which has seen its fair share of highlights already.

These highlights include beating the Steelers in Pittsburgh for the first time since 1986, which had second-year quarterback Patrick Mahomes light it up for a total of six touchdown passes, which has been the main contribution to his MVP-like start to the year. He leads the NFL with 14 touchdown passes through five weeks.

The Chiefs also overcame a 10-point fourth-quarter deficit to the Denver Broncos on the road on Monday Night Football, which was actually the first time in 65 games that the Broncos had lost a game after leading by double-digits in the fourth quarter.

Then last week, facing a Jaguars' defense that hadn't allowed a touchdown in the first half or a 300-yard passer in 15-straight regular-season games, the Chiefs accomplished both.

Now, the test gets even more difficult traveling to Foxboro, where the Patriots have won 53 of their last 57 games against AFC teams in the regular season.

Here are five things to watch on Sunday night:

1.    The Chiefs are banged-up in the secondary

The Chiefs have been without two of their starting safeties in Eric Berry and Daniel Sorensen for the entire season. Berry is dealing with a sore heel and hasn't practiced since the first week of August, and Sorensen was injured at training camp and was subsequently placed on Injured Reserve. He's able to return for the game against the Cleveland Browns at the earliest.

And then just last week, two of the next safeties in line for the Chiefs' defense—Eric Murray and rookie Armani Watts—both left the game with injuries. Neither of them will play this week against the Patriots.

The Chiefs will go out there with veteran Ron Parker, Jordan Lucas, who came over in a trade with the Miami Dolphins at the end of the preseason, Josh Shaw, who was picked up earlier this week, and Leon McQuay, who was brought up from the practice squad on Saturday.

It's a challenge for a defense that's facing arguably the greatest quarterback in NFL history in Tom Brady, who's a guy who will find the matchup that favors the offense every single time.

There's confidence expressed in all of those players to be able to step in and make plays, and we saw that with Lucas last week when he finished the game with seven tackles, which was third-most on the team. He had one of the three red zone interceptions off Jaguars' quarterback Blake Bortles in that game, but in any case, the lack of playing time for those guys with each other makes the Chiefs' secondary, particularly at safety, something to watch on Sunday night.

2.    The Chiefs have gotten out to fast starts, and the Patriots have too…in the games they won

Here are six stats to know for Sunday night:

3.    How do the Chiefs handle Patriots' running back James White?

The Patriots' offense is built upon the short passing game—that's what Brady and this group has done for the last few seasons. His Pro Football Focus "accuracy rating" on deep passes this year is 36.4 percent, which ranks 28th in the league, although the continued development and playmaking of the recently-acquired Josh Gordon will undoubtedly improve these numbers moving forward.

In any case, James White is the Patriots' most-targeted receiver this year with 44 total targets through five games, and if the Patriots feel as though they have an advantage with White in space on the Chiefs' safeties and linebackers, then we can expect to see a lot more targets thrown his way.

Through five games this year, the Chiefs' defense has allowed 36 receptions for 427 yards and three touchdowns to opposing running backs.

4.    Who steps up for the Chiefs' offense?

The talk all week has been about how good Belichick is at tailoring his defense each week to the offense that they're playing, and while that's pretty common for teams to do from a surface-level point of view, the facts of the matter are Belichick is just better at it than everyone else. It's why he's the third-winningest coach in NFL history with 281 career wins.

But the guy he's facing in this chess match on Sunday night—Andy Reid—is pretty good at this, too. Reid is actually going for his milestone 200th win on Sunday night. He's currently ninth in NFL history with 199 career wins.

Belichick is known for his ability to take away teams best (and first) offensive options.

Last year in the Chiefs' Week 1 victory over the Patriots, the world didn't yet know about running back Kareem Hunt, who finished the game with 246 total yards of total offense and three touchdowns.

And while people may know all about him now after he led the league in rushing last year, that doesn't necessarily mean it's a slam dunk that all of the Patriots' defensive efforts will be in stopping the Chiefs' running game, and that's because they also possess one of the league's deadliest passing attacks.

In Week 1 against the Chargers, it was Tyreek Hill who led the charge—snagging seven receptions for 169 yards and two touchdowns. The next week against the Steelers—both Travis Kelce and Sammy Watkins went over 100 yards, with Kelce bringing in two touchdowns as well.

There are multiple guys on this Chiefs' offense who can beat you in any given week, and for Mahomes, the only challenge is to find the right guys against the right coverages, they'll do the rest.

"They're going to have a game plan on trying to stop some of your better guys," Mahomes explained earlier this week of the Patriots' defense. "With us, I feel like the mentality we've had this entire season is that whoever is open, give them the ball and let them make the play. They are going to do some stuff to try to confuse me, but I am going to try to maintain our game plan and keep working."

5.    With De'Anthony Thomas' injury, who might we see returning kicks?

During Thursday's practice, the Chiefs were dealt a tough blow as receiver and special teams' standout De'Anthony Thomas was injured in what was described as a "freak accident."

Thomas was stepped on from behind and re-fractured the same leg that was injured in the Week 17 game at Denver last season. There was no damage to the rods that were placed in his leg following that injury and subsequent surgery, but he will be out for some time even though this particular injury won't require surgery.

So, with Thomas out, the question remains of who might be returning kicks for the Chiefs on Sunday night?

The most likely option would be rookie sixth-round pick Tremon Smith—the lightning-fast cornerback out of Central Arkansas who has drawn plenty of praise from Assistant Head Coach and Special Teams Coordinator Dave Toub over the past few months. He has yet to return a kick in the regular season after returning eight kicks for 198 yards (24.75 ypr) in the preseason.

Chris Conley and Demarcus Robinson could be other options as well.

The Chiefs have been the league's best special teams' unit this season. Kicker Harrison Butker hasn't missed a field goal in seven attempts, punter Dustin Colquitt leads the NFL with a net average of 45.1 yards per punt, and the average starting field position for opponents against the Chiefs is the 23.5 yards line, which is the best mark in the NFL.

And even though Thomas is out and was one of the top special teams' players for Toub's four units, the team did go out and re-sign veteran outside linebacker Frank Zombo this week. Zombo has been one of Toub's best players over the past five seasons.

On Friday, Zombo, who was released at the end of the preseason, said he had other options and places to play but wanted to stay available for the Chiefs, who had told him that they'd bring him back at some point this season.

Zombo waited for that call, and it came this week.