Indianapolis ? It may be a stretch to say the fifth game of the NFL season is a must-win for a team with the pedigree and recent history of the Indianapolis Colts.

Guess what? It’s time to stretch.

The Colts need a solid win over the Kansas City Chiefs this Sunday as desperately as they’ve needed any win in a long, long time.

If they lose this game, their fans might as well order the Chicken Little costumes for Halloween. The sky will be falling.

The Colts are 2-2. Their defense has been inconsistent at best, porous at worst. They’ve lost two safeties Bob Sanders and Melvin Bullitt to long-term injuries. They’ve been banged up on the offensive line and at receiver.

What’s the opposite of a smooth start?

Well, that’d be the San Francisco 49ers. But the Colts are on a rocky road in unfamiliar territory.

“I think guys are disappointed, frustrated, all normal reactions,” quarterback Peyton Manning said. “I think those can be healthy reactions and moods.”

This is a huge test because the Chiefs (3-0) are the last remaining unbeaten team in the NFL. They aren’t the easy-mark Chiefs of recent vintage, either. Clutch performers such as Mike Vrabel and Thomas Jones are in uniform these days. The coordinators are a pair of classic Patriots: Charlie Weis on offense and Romeo Crennel on defense.

The Chiefs also have had an extra week to prepare. The Colts have no time to stew.

If the Colts can beat the Chiefs and go on the road and grab a win in a tough environment in Washington on Oct. 17, they’ll enter the bye week with a 4-2 record.

If they lose at home, showing further vulnerability, they’re staring at a potential 2-4 start. That would be ugly.

So, first things first. The Colts have to find a way to replace Bullitt at safety. Among the candidates are rookie Brandon King from Purdue, third-year pro DaJuan Morgan, a pickup from the Chiefs of all teams, and free agent Aaron Francisco, who played for the Colts last season.

Morgan stepped into Bullitt’s place after he left the game at Jacksonville last weekend and seems the most logical choice to earn the starting berth. He may even have a little edge, having been with the Chiefs for the last two seasons.

The Colts expect the Chiefs, third in the NFL in rushing offense, to come out and try to engage in a smash-mouth ground control approach. Jamaal Charles is averaging 7.0 yards per carry as the Chiefs’ leading rusher, Jones is at a solid 4.2 yards per carry. As a unit, they’re averaging 160 yards per game.

The Colts had issues slowing Houston and Jacksonville on the ground in their two losses.

Unless the Colts can stop, or at least slow, the run, the vaunted pass rush of Dwight Freeney and Robert Mathis will continue to be dormant.

They have spent little time in the opposing backfield the last two games in a win over Denver (when the Colts gave up 476 yards passing) and the loss to Jacksonville.

Colts coach Jim Caldwell said he believes the frustration and uneasiness in the locker room after the 2-2 start can be used to the Colts’ advantage.

“As much as we’ve won around here, (the frustration) is highly unusual for us, but I don’t think it’s a bad thing,” Caldwell said. “We know we have to be better.”

The Colts’ schedule after Kansas City and Washington gets tougher, with no real relief in sight.

That’s why it’s essential the third win comes Sunday.

“If we go out there and play our ball, limit our mistakes and don’t beat ourselves, it’ll be very tough to beat us,” safety Antoine Bethea said.