Brandon Flowers and Javier Arenas were often in position, but because they are a half-foot shorter than Thomas and Decker, they couldn't stop the Denver receivers. The pair combined for 14 catches, 198 yards and three touchdowns on Dec. 30, 2012, in a lopsided Chiefs defeat, 38-8.
When new general manager John Dorsey and coach Andy Reid joined the Chiefs in January, one of their first priorities was to look for corners who could not only look players such as Thomas and Decker in the eye, but get physical with them as well.
"The No. 1 thing in corners is coverage," Chiefs defensive coordinator Bob Sutton said. "It's just like receivers. The No. 1 thing is the ability to get open. But if you're bigger and can get open, that's even better. With corners that are bigger and can cover, that's even better."
The Chiefs signed Sean Smith as a free agent, and at 6-3, he's one of the league's tallest cornerbacks. They also claimed off waivers 6-2 rookie Marcus Cooper, who has been a find. Flowers also plays and will likely cover Denver slot receiver Wes Welker who, at 5-9, is Flowers' size.
The Chiefs are confident what happened last year against Decker and Thomas won't be repeated in Denver on Sunday night when they play against the Broncos again.
"It's going to be a tough challenge, but I feel like we've got the players to get it done," Flowers said.
Smith has been a key figure for the Chiefs all season. He has allowed them to play the press man-to-man coverage that Sutton prefers, and Smith's 100-yard interception return was the crucial play in the win against the Bills in Buffalo two weeks ago.
But it's not an oversimplification to say that when boiled to its essence, Smith was signed with the matchups against Thomas, Decker and the Broncos in mind. The teams are fighting for first place in the AFC West and meet again on Dec. 1 in Kansas City.
And there could be a third game between the teams in the postseason.
"I can see how you can look at it that way," Smith said. "But I think it's more that the Chiefs wanted to bring in some big, physical cornerbacks, some guys who can play well in all the games. It's not just about the Broncos. This team was trying to win some more games and do some big things. I'm just a small piece of that."
More accurately, he's a big piece of it.
"Sean is a huge man," Reid said. "He's the size of a linebacker, really."
Smith's length, as well as that of Cooper, could make a big difference. Given the accuracy of Denver quarterback Peyton Manning, who can often put the ball exactly where he wants it, having a tall cornerback could make the window very small in which he needs to fit the ball.
"It gets down to a game of contested throws," Sutton said. "You have to contest those plays. You have to challenge them."
The Chiefs pulled Cooper off waivers from the 49ers days before the start of the regular season. A former wide receiver at Rutgers, Cooper almost immediately claimed playing time by showing strong instincts, good ball awareness and excellent ball skills.
Smith and Flowers are the starters, but Cooper plays when opponents send an extra receiver on the field.
"He'll be all right," Smith said when asked how Cooper will fare against Decker and Thomas. "He's come in and worked hard and gotten better every day, so his confidence is very high right now. He's playing some good ball. This week shouldn't be any different for him. We definitely hold him to the same standards as everybody else on the defense."
It doesn't hurt Cooper that he's tall, at least in the minds of the Chiefs. Dorsey prefers bigger, taller cornerbacks. It's not a coincidence that Arenas, one of last year's starting cornerbacks, was traded to the Arizona Cardinals in the spring.
The Chiefs knew how he matched up with bigger receivers in general and Decker and Thomas in particular. Even over in Denver, Manning has noticed the change in Kansas City's secondary.
"I don't know how much height comes into play," Manning said. "Either the guys can cover or they can't cover, and these guys can cover. They're good players and they're playing well."