Kansas City, Mo. ? A loss to Cincinnati did more than ruin the Kansas City Chiefs’ perfect record and slice its lead for home-field playoff advantage to just one game over New England, Indianapolis and Tennessee.

It also highlighted a dangerously weak run defense, a season-long problem obscured by the glow of victories in the Chiefs’ first nine games.

Rudi Johnson, the Bengals’ 220-pound running back, flattened tacklers while gobbling up 165 of Cincinnati’s 200 rushing yards.

Although statistics can be deceiving, the Chiefs this week rank 25th in the league in rush defense, allowing an average of 130.5 yards. The Chiefs are yielding 4.9 yards per carry, next-to-last in the NFL.

“It’s that kind of leaky yardage we’ve got to stop,” linebacker Shawn Barber said. “Tackling is just taking the extra two or three steps at the end of a play and making sure you wrap the guy up and finish the play. I’m probably one of the biggest violators when it comes to not finishing plays.”

The Chiefs have faced some of the league’s top backs — Jamal Lewis, LaDanian Tomlinson, Ahman Green, to name a few — and every one had a game to remember. Next up is the Oakland Raiders’ Tyrone Wheatley, who ran for 109 of the Raiders’ 191 yards rushing in a victory last week over Minnesota.

“We’ve had a problem stopping the run. It’s been more of a problem on first down than any other down. But it is a problem,” coach Dick Vermeil said Tuesday. “We gave (Cincinnati) 92 yards on two snaps. One of them should have been a minus-yardage play and the other one should have been a six-yard play.

“But in both situations, we didn’t tackle. And when everybody else is committed to a blitz we were in, you have to fulfill your responsibility and it didn’t get done.”

The Chiefs have given up 39 runs of 10 yards or more, but only seven runs of more than 20 yards. The reason may be safety Greg Wesley, who is combining with Jerome Woods to give the Chiefs one of the best safety combinations in the league.

But Vermeil indicated there had been no single cause for the run-defense breakdown.

“A percentage of them is the result of a good running back and not getting him down, a ricochet runner,” he said. “Some of them were just well blocked football plays. Those guys are getting paid, too.”