Indianapolis ? Tony Dungy won’t change his philosophy.

He intends to play his regulars this week, build momentum for the playoffs and try to put the Indianapolis Colts in the best possible playoff position – even though they no longer control their seeding fate.

“We’ve got to treat this like a must-win game,” he said Monday. “We need to win to stay ahead of New England and put pressure on Baltimore.”

A month ago, the Colts (11-4) appeared headed toward earning a second straight No. 1 seed in the AFC playoffs. Their late-season collapse has ruined everything.

Back-to-back losses at Tennessee and Jacksonville left San Diego in the lead for home-field advantage, and Sunday’s demoralizing loss at Houston may have cost Indy a shot at the coveted first-round bye, too.

More troublesome are the problems that seem to get worse with each passing week.

The league’s worst run defense took another hit Sunday when Ron Dayne rushed for a career-high 153 yards and two touchdowns – only the third 100-yard game of the former Heisman Trophy winner’s seven-year career.

By successfully playing keepaway, opponents also have managed to beat two-time MVP Manning the one way he can’t control: making him a spectator. Manning has spent more time in recent weeks studying photos on the sideline than picking apart defenses on the field.

And four losses in six games, including four straight on the road – another ignominious first during Dungy’s Indy era – have left the Colts in the unenviable position of trying to turn things around in the playoffs.

It’s an unusual predicament for the first team in NFL history with consecutive 9-0 records, which is not accustomed to watching the scoreboard in late December.

“I don’t think it’s confidence, I think there’s disappointment and frustration that we’re not getting it done,” Dungy said. “We have to fix it if we want to get where we want to go.”

Dungy insists the Colts can still get it right in time to make a Super Bowl push. He might use this year’s St. Louis Cardinals as an example of how to change perceptions in the postseason.

Many figured the Cardinals’ poor closing stretch would produce an early playoff exit in baseball’s playoffs. Instead, they won the World Series.

Clearly, though, time is running short.

The Colts close the regular season Sunday at home against Miami before likely opening the postseason against an AFC wild-card team. The worries are mounting.

Only a victory over the Dolphins and a win by Buffalo at Baltimore would give Indy the No. 2 seed.

But the uncharacteristic scenarios are also creating some unusual moments for these Colts.

Dungy called the Houston loss his most disappointing in five seasons with Indianapolis because he thought his team played like nothing was at stake.

Manning was even caught by television cameras pleading with the defense to give him another chance late in the third quarter, something Dungy said the defense was already telling itself.

“I think we’re all frustrated to a certain point, and we didn’t get it for him enough yesterday,” Dungy said. “But nobody’s more frustrated than the defense.”

With so much still at stake, Dungy has no intention of using this week to rest starters and even hopes injured safety Bob Sanders (knee) and tight end Dallas Clark (knee) can play against Miami.

“That would be a best-case scenario,” Dungy said. “We’d like to get Bob and Dallas some work before the playoffs, but we’re not going to rush them in there if they’re not ready.”

Starting left guard Ryan Lilja also sprained his right knee Sunday, and Dungy said he wasn’t sure whether he would play.

The one certainty for Dungy is that to prevent another big goal from slipping away, the Colts’ much-maligned defense must improve now.

“We can’t let allow the disappointment of not keeping things in our own hands to get to us,” he said. “We’ve got to play with the energy and emotion we played with (last) Monday night and then string together three or four in a row like that.”