INDIANAPOLIS — The Pittsburgh Steelers beat the Indianapolis Colts three times. Only the third one stuck.

In one of the zaniest yet thrilling conclusions the NFL has seen, the Steelers won their sixth straight game Sunday, becoming the first sixth seed to advance to a conference championship game by beating the Colts 21-18.

When the Steelers (13-5) catch their breath, they'll head to Denver for their sixth AFC title game in Bill Cowher's 14 seasons as coach. The winner of next Sunday goes to the Super Bowl, which Pittsburgh hasn't appeared in since 1996.

This one looked easy after a superb game plan helped the Steelers to a 21-3 lead. Then, things went haywire.

"That is one of the craziest games I have been in," linebacker Joey Porter said.

"It went from an all-time high to an all-time low back to an all-time high," Hines Ward added.

And, in a span of about five minutes.

Pittsburgh led 21-10 lead on Ben Roethlisberger's two touchdown passes in the first quarter, and Jerome Bettis' 1-yard vault in the third.

All-Pro safety Troy Polamalu's diving interception of Peyton Manning's throw at the Pittsburgh 48 with 5:26 remaining seemed to seal the Steelers' fifth consecutive postseason victory over the Colts. But when he got up to run and fumbled the ball, then recovered, Colts coach Tony Dungy challenged.

Somehow, despite a dozen replays showing Polamalu's catch, the call was overturned by referee Pete Morelli.

"I know they wanted Indy to win this game; the whole world loves Peyton Manning," Porter said. "But come on, man, don't take the game away from us like that."

Especially when the Steelers were finding ways to give it away.

Manning's completions of 20 yards to Marvin Harrison and 24 to Reggie Wayne set up a 3-yard touchdown run by Edgerrin James. A 2-point conversion pass to Wayne made it 21-18.

Indy stopped Pittsburgh's offense, but with 1:20 remaining, Manning was sacked for the fifth time at his 2. On the Steelers' sideline, players were jumping and dancing and pumping fists.

So was Cowher, whose brilliant game plan — pass first on offense, contrary to style, and apply constant pass rush pressure on defense — ordered the ball handed off to Bettis. Cowher figured a touchdown from there was inevitable for the Bus, who has nine TDs since a Nov. 26 loss at the RCA Dome.

"They had three timeouts," Cowher reasoned. "At that point, the last thing I thought we would do is fumble with Jerome Bettis."

That's just what the surehanded Bettis did when popped by linebacker Gary Brackett. Nick Harper, whose knee was cut with a knife Saturday in an apparent domestic dispute with his wife, grabbed the ball and headed toward a highly improbable winning touchdown.

But Roethlisberger gave chase, tumbled, reached out a hand and made a saving tackle at the Indy 42.

"Once in a blue moon, Jerome fumbles," Roethlisberger said. "Once in a blue moon, I make a tackle. They just happened to be in the same game."

The stunned fans, prepared to head for the exits seconds before, were ecstatic. Two passes got the ball to the Pittsburgh 27, and Mike Vanderjagt lined up for a 46-yard field goal to send it to overtime.

Wide right.

Vanderjagt then slammed his helmet to the turf, obviously forgetting how fortunate he was to have the chance.

"It's extreme disbelief," Vanderjagt said. "From the Polamalu interception reversal to Jerome's fumble, everything seemed to be lined up in our favor. I guess the Lord forgot about the football team."

The Colts (14-3) can forget their first Super Bowl trip representing Indianapolis. They're left to wonder where the magic of a 13-0 start went.

"The disappointing thing is that we played really well this year for a number of games," Manning said. "But certainly two of the last three games here, San Diego and Pittsburgh, we got outplayed. There's no question it's disappointing. There is no question we were in good position with home field and having the bye.

"At this point, it is hard to swallow."

It was the first time the Steelers won two straight playoff road games; the beat AFC North winner Cincinnati in the wild-card round.

"The play-calling was aggressive," Ward said. "They thought all we can do is run the ball. We can pass the ball, too."

Antwaan Randle El's 6-yard TD reception for a 7-0 lead was his first since the season opener, hardly an impressive stat for a starting receiver. But it capped one of Pittsburgh's most impressive drives of the season, 84 yards in 10 plays, with seven passes, including 36- and 18-yarders to rookie tight end Heath Miller.

Ward broke two tackles on a 45-yard completion, leading to Roethlisberger's 7-yard TD pass to Miller to make it 14-0.

The Colts marched 96 yards in 15 plays, taking up nearly 10 minutes of the second period, but their best drive, on which Manning went 6-for-6, ended with only Vanderjagt's 20-yard field goal.

But his next attempt, the one that would have forced overtime — and who knows what else in this wild affair — never had a chance.

It was a sad ending for Dungy, whose son died of an apparent suicide last month. Dungy's team clearly was the NFL's best for 13 weeks. But in the most important weeks, the Colts faltered.

Notes:

Morelli's explanation of the reversal: "I

had the defender catching the ball. Before he got up, he hit it with his leg with his other leg still on the ground. Therefore, he did not complete the catch. And then he lost the ball. It came out, and so we made the play an incomplete pass." ... Colts TE Dallas Clark showed excellent burst on a 50-yard TD pass play.