It was Week 3.
On first-and-goal from the 8-yard line late in the first quarter, Green Bay Packers quarterback Aaron Rodgers scrambled up the middle for a gain of 5 yards before being tackled by linebacker Tamba Hali.
In the back of the end zone, second-year cornerback Phillip Gaines was on the ground holding his knee. A non-contact injury ultimately showed itself to be a torn ACL for the speedy former third-round pick out of Rice.
Just like that, Gaines, the team's starting nickelback (slot corner), was lost for the season.
Moving forward, the Chiefs would rely on the versatility of fifth-year player Ron Parker, who had already moved around from cornerback to safety multiple times in his three seasons with the club.
But he didn't have much experience playing on the inside.
"That's a whole different world in there when you get inside," Chiefs coach Andy Reid explained of Parker moving to nickelback. "I'm proud of him for the job that he's done. It's not easy. We saw him do it our first year, against San Diego, and again, it's not an easy thing to do."
Parker ranks second on the team with 72 tackles this season.
"His flexibility is huge for us," Reid added. "He can play corner, he can play nickel and he can play safety. That's a pretty good deal."
The move inside wasn't necessarily a smooth transition for Parker. It's something he had to work hard to improve at during a time when the team didn't have much room for error after dropping five of their first six games.
"At first, I started out kind of slow and I needed a little help," Parker explained, "so the coaches did a good job of going over the stuff with me and putting me in a position to make plays."
Despite being lost for the season with the injury, Gaines still found a way to help the guy who would be replacing him on the inside.
"My first two weeks playing nickel, [Gaines] probably came over to my house like 10 times," Parker explained. "We spent a lot of time together."
After practice had ended and players had all left the building to head home, Gaines headed over to Parker's house to help him learn a new position.
"He just helped me out with all of the decisions I had to make," Parker explained. "He'd just tell me the best way to play different situations."
Parker has figured things out and the Chiefs defense has coincidentally gotten better at the same time.
Over the past nine games, Parker has picked up 5 sacks from his slot cornerback position, including one on Sunday over the Oakland Raiders.
With the 2 sacks he already had coming into this season, Parker's 7 career sacks are now a franchise record for a defensive back.
It was a record previously held by safety Reggie Tongue, who played for the Chiefs from 1996-99.
"That's a great feeling man," Parker said of breaking the record. "I knew I was close. I was joking with (defensive coordinator) Bob Sutton earlier in the week and telling him that he needed to dial up some blitzes so I could get it.
"We laughed about it but we all got the job done."
Much of Parker's success can be attributed to the unselfish ways of Gaines, who went out of his way to help Parker try and make as smooth of a transition as possible for the overall success of the defense.
"Gaines is a good kid and you wouldn't expect anything less than that from him," Reid explained. "That's just how he rolls. He's smart too. That's just the unique part of this team.
"They all work together."
Parker spoke about some of the differences he's noticed playing on the inside.
"You have to know the game," Parker explained. "You have to know route concepts and that's something I'm comfortable with—reading formations and sets.
"That has played a big part and you have to know where your help is at."
But sometimes, the ability to step up and make a play is just instinctive.
That was the case of Parker's interception of Derek Carr late in the first half on Sunday, when the Chiefs were holding on to a 14-3 lead.
It was Parker's 3rd interception of the season.
"I saw Carr scrambling in the backfield and he was looking over at [Amari] Cooper sitting in the honey hole behind Sean [Smith]," Parker explained. "[Smith] went up to rush him and I replaced him, and then I saw him get ready to chuck it up there and so I just went and made a play on the ball.
"It felt great to come down with that one."
Parker's ability to not only make plays, but also to simply be available for wherever he's needed has been an invaluable asset to the Chiefs defense over the past three seasons.
"To be honest with you, I don't even know where Ron [Parker] is playing sometimes," defensive lineman Dontari Poe explained, "but I know that he's always on the field and he's always locking it down."
Parker has played more snaps than anyone not named Derrick Johnson on a defensive unit that ranks No. 2 in the NFL in scoring this season.
He's probably not getting enough credit for what he's done.
Photos from Chiefs Week 17 matchup against the Raiders