Kansas City, Mo. ? They’ve brainstormed, soul-searched, and studied film until their eyes turned bleary.

In their quest for an answer to this perplexing mystery, they’ve bounced theories off each other and off the wall.

Still, nobody can solve Kansas City’s case of the disappearing third quarter.

“In the fourth quarter, we’re OK,” said a frustrated head coach Herm Edwards. “It’s just that one little quarter for some reason.”

In the last seven games, starting when their quarterback situation stabilized and they became more or less competitive, the rebuilding Chiefs (2-11) have taken the lead into halftime on four different occasions. In another game, they were tied.

But they’re 1-6 in those games, largely due to the fact they’ve been outscored in the third quarter, 53-13. In the fourth quarter, the cumulative score is a reasonable 37-37 tie.

Edwards has changed halftime routines, changed the music that’s piped in and even contemplated just staying on the field.

But nothing seems to work. Last week at Denver, the Chiefs led the Broncos, 17-14, at halftime but squandered a great scoring opportunity in the third quarter and wound up losing, 24-17.

“We had a chance to put some points on the board from the 30 and we go backward,” Edwards said. “It was the third quarter again.”

Another good example was Nov. 9 in San Diego. With Tyler Thigpen throwing touchdown passes to Mark Bradley and Tony Gonzalez, the Chiefs went into halftime leading 13-6. But shut out in the third quarter, they lost, 20-19.

Now the Chargers are back for a rematch today in Arrowhead Stadium and the Chiefs are still groping for answers to the third-quarter woes that haunted them in San Diego.

“You throw around your ideas,” Gonzalez said. “Herm, he was really attacking that third quarter for a couple of weeks. We were talking about it, (saying) ‘We’re really going to come out in the third quarter!’

“But we still come out there and don’t play well. I don’t know what it is. Maybe it’s the young players not keeping their focus. Maybe it’s the coaches not staying as aggressive. It seems like we’re playing just as hard. But it’s been our Achilles’ heel.”