The Kansas City Chiefs (5-1) lost their first game of the season Sunday night at Gillette Stadium in Foxboro, Massachusetts, falling to the New England Patriots (4-2) by a score of 43-40.

Here are 10 observations from the game:

1. The Chiefs' comeback bid fell just a bit short

They trailed by 15 points at halftime and despite a strong second-half effort, which saw the Chiefs take a lead at one point for a brief minute, the Patriots drove down the field with less than two minutes remaining and kicked a game-winning 28-yard field goal to walk off with the 43-40 win.

Chiefs' quarterback Patrick Mahomes showed some moxie in the second half—atoning for a first half in which he tossed a couple of interceptions, but the 23-year-old came back in the second half to complete 9 of 13 passes for 188 yards and four touchdowns. 

Tyreek Hill was the beneficiary of three of those scores as he finished with seven catches for 142 yards and three touchdowns.

One final note on the overall game, Kicker Harrison Butker has had a fantastic start to the season—hitting all four of his field goals tonight and all 11 so far this season.

2. Mahomes' 75-yard strike to Tyreek Hill was ridiculous

The fourth quarter of the game resembled that of a ping-pong game in which each side just kept making plays and putting the ball in the court of the other, who would respond in kind and they'd keep going back and forth.

After the Patriots kicked a field goal and took a seven-point lead with just over three minutes left in the game, Mahomes and the Chiefs' offense didn't take long to respond.

On the very first play for the Chiefs' offense, Mahomes hit Hill deep down the field, and then Hill, who had to jump up to catch the ball, accelerated with a speed and burst that isn't possessed by many people in the world and raced down the left side of the field for a 75-yard touchdown. 

Following the Harrison Butker extra point, the Chiefs had tied the game, 40-40.

The Patriots would respond again, though. 

Patriots' quarterback Tom Brady finished 24 of 35 for 340 yards and a touchdown, leading their offense to 500 yards in total and making several big-time throws when called upon.

3. Tremon Smith's 97-yard return set up a late go-ahead touchdown

With special teams' ace De'Anthony Thomas suffering a leg injury late in the week in practice, that meant rookie sixth-round pick Tremon Smith assumed kick return duties for the Chiefs, and it proved to be huge on Sunday night.

Early in the fourth quarter with the Chiefs trailing by four points after a key defensive stand, which culminated with a nice play by defensive lineman Jarvis Jenkins, who was able to get pressure in the face of Brady and caused the pass to fall incomplete—leading to a field goal, the subsequent kickoff became a huge play in the game.

Smith took the kickoff through the right side and exploded down the field for a 97-yard return that set up the Chiefs' go-ahead touchdown, which had Mahomes throw a "floater" to Hill on third down.

After trailing by 15 points at halftime, the Chiefs had taken the lead with less than 10 minutes to go in the game.

4. Patriots responded again after the Chiefs took the lead

After the Chiefs took the lead on the Hill 1-yard touchdown reception, Brady and the Patriots' offense responded. 

They went 75 yards on seven plays in just over three minutes and the drive culminated with a four-yard touchdown on a scramble from Brady, who leapt into the end zone after breaking a tackle in the backfield.

The key play on the drive was a 42-yard completion from Brady to Chris Hogan on third-and-1.

5. Kareem Hunt puts up big numbers at Gillette Stadium once again

In the Week 1 matchup with the Patriots last year, Hunt had 246 yards of total offense with three touchdowns to help the Chiefs to that decisive win over the Patriots. It was Hunt's introduction to the country after being inserted into the starting role with Spencer Ware's injury late in the preseason.

Hunt went on to lead the league in rushing, but it was that first game against the Patriots that got everyone's attention, and he had it again on Sunday night. 

Hunt finished with 185 yards of total offense (80 rushing, 105 receiving), including one touchdown.

6. Chiefs' offense comes up with a huge play to begin second half

With the Chiefs' offense facing a third-and-3 from their own 37-yard line on their first drive of the second half, Mahomes left the pocket and rolled to his right and found Hunt deep down the right sideline for what turned out to be a 67-yard touchdown strike, which got the Chiefs back to within one possession at 24-16.

It was their first touchdown of the game and the right response to a tough first half on both sides of the ball.

7. Breeland Speaks with a big play for the Chiefs' defense

On the ensuing Patriots' offensive drive following the 30-yard field goal from Harrison Butker, which brought the game to within one possession at 29-17, the Patriots faced a third-and-10 from their own half of the field.

Brady sat in the pocket for a while as the Chiefs' defensive backs did a great job of covering down the field, and then rookie Breeland Speaks made the biggest play of his young career with a strip-sack fumble of Brady as veteran defensive lineman Allen Bailey hopped on the ball.

It gave the Chiefs' offense great field position, which they took advantage of very quickly.

8. Chiefs' offense responds after the takeaway

After a couple of plays, which included a 15-yard strike to Sammy Watkins across the middle, Mahomes found Hill deep down the middle on a little corner route for a 17-yard touchdown.

It was the perfect response to the defense stepping up and giving them great field position.

Following the touchdown and subsequent extra point, the Chiefs then trailed, 27-26.

9. Patriots got off to a fast start, led 24-9 at halftime

The Chiefs struggled on both sides of the ball to begin Sunday's game, and there's no need to look any further than the three "core" stats that are often considered the keys to victory—red zone efficiency, third-down conversions, and turnover differential.

At the end of the first half, the Chiefs were losing all three of those areas to the Patriots.

The Chiefs were 0-2 inside the red zone, committed two turnovers on Mahomes' interceptions, and converted just 2 of 5 third downs.

The Patriots, on the other hand, were 3 for 3 inside the red zone, converted 2 of 4 third downs and didn't commit a turnover.

That's the main difference with their 24-9 lead at halftime.

10. Chiefs played with several key starters out of the game

The Chiefs were without four of their top safeties (Eric Berry, Eric Murray, Armani Watts, Daniel Sorensen), two edge rushers (Justin Houston, Tanoh Kpassagnon) and two of their starting offensive linemen (Laurent Duvernay-Tardif) after center Mitch Morse left the game early with a concussion.

They had a chance late and made a game of it and they expect the guys on the field to make plays, but the injuries are mounting up for the Chiefs, particularly on defense.