Had Richie Petitbon known before the 1989 season that his starting lineup would go through five cornerbacks, three middle linebackers and his best pass rusher, that his original plan would be in ashes by midseason, he might have guessed disaster was on the horizon.

He would have guessed wrong. The Washington Redskins took the worst of circumstances and turned them into the best of defenses.

After watching his starting lineup peeled away by injuries, suspensions and poor performances, Petitbon, the Redskins' assistant head coach and defensive architect, put together a defense that was almost perfect down the stretch.

It allowed a total of 10 second-half points the last seven games, and the Redskins can thank their defense for victories over Atlanta, Phoenix, Chicago and Philadelphia.

That quality of play has carried over into this season despite the Redskins starting only three players -- Charles Mann, Wilber Marshall and Darrell Green -- who probably could start for anyone and a lot of others who know their roles and play their situations well.

It's hard to appreciate on paper, easier on the field, where they've allowed one second-half touchdown in their last nine games. They had allowed one second-half field goal in that span until San Francisco's Mike Cofer kicked two during Sunday's 26-13 loss.

As the Redskins prepare for the Dallas Cowboys Sunday at RFK Stadium, they've allowed an average of 1.8 points and 148 yards in the second half of those nine games.

"The defense has just been tremendous," Coach Joe Gibbs said. "Richie and those guys have really done a good job."

Petitbon agrees but isn't certain he knows why: "Who knows what the key is? We gave up some yards against San Francisco, but I think those guys played about as well as they can play. They'd had a bad week in New Orleans and they came out like they were scared. They had something to prove, and I'd be surprised if they can do much more than that."

What happened to make the defense play so well? Not much good.

Green went to the sideline with a broken wrist. Markus Koch bruised ribs. Dexter Manley and Barry Wilburn were suspended. Brian Davis was benched. Neal Olkewicz was phased out.

When the juggling finished, the worrying began. The Redskins had a pair of pint-sized cornerbacks (Martin Mayhew and A.J. Johnson), a rookie tackle (Tracy Rocker) and a Plan B end (Fred Stokes). Kurt Gouveia took over for Olkewicz in the middle, then got hurt and gave way to Greg Manusky. Linebackers coach Larry Peccatiello says of Gouveia and Manusky: "They get the absolute maximum out of their talent. What they need beyond that, they can't get. Only God could make Manusky faster or Gouveia bigger."

People moving out, people moving in.

"You really had no idea what was going to happen," Petitbon said. "All you can do is tell guys to play hard and hope they all jell."

Which may have been the key. The Redskins say one of the reasons for their success is that they were so far down they had no place else to turn. They knew unless they hustled to the ball, helped one another out and played with a frenzy they'd be blown away.

They also were coming off that 13-3 loss to the Cowboys, the week that Gibbs calls "probably my lowest in 10 years here."

"It came down to trusting the guy next to you," safety Todd Bowles said. "We didn't know how good or bad we were going to be, but we knew we could hustle and play hard. A lot of times, if you play hard, you'll have good results."

Their streak began in Week 10. A week after losing to the previously winless Cowboys, the Redskins went to Philadelphia and shut down the Eagles, 10-3. Randall Cunningham and the Eagles drove past midfield only twice.

Their deepest drive was to the 19-yard line, where on third and three, Gouveia intercepted Cunningham's pass.

The Redskins didn't know it at the time, but a pattern had begun that has extended through the first two games of this season. The Eagles gained only 16 yards rushing the second half. Forced to pass, the Eagles gained some yards (119).

But the Redskins also came up with a big play at an opportune time.

The next week in a 14-10 loss to the Denver Broncos, the Redskins threw another second-half shutout. The Broncos, with Gary Kubiak playing quarterback after John Elway got sick, drove to the 39 twice, and Kubiak twice missed an open Vance Johnson. They didn't get any closer.

A week later, there was another second-half shutout during a 38-14 victory over Chicago. The Bears drove to the 31 and Monte Coleman came up with an interception. A series later, Davis got one. For the day, Coleman had a sack, an interception and a fumble recovery. The Bears gained six yards rushing after halftime.

In Week 13, Johnson returned Tom Tupa's pass for a second-half touchdown, Wayne Davis intercepted one in the end zone and the Redskins rolled past the Phoenix Cardinals, 29-10. The Cardinals were a yard better on the ground than the Bears had been a week earlier.

Two weeks later, the Chargers became the only team in the streak to score a second-half touchdown. But the Redskins won, 26-21, after Mann recovered quarterback Billy Joe Tolliver's fumble to set up the winning touchdown.

By that time, the Redskins were on a roll -- and knew it.

"We had a good feeling," Bowles said. "We had a feeling that we thought something good was going to happen."

Against the Atlanta Falcons in Week 15, a lot of good things happened again. The Falcons kicked a second-half field goal, but the third quarter began with: Mann sacking Chris Miller to end a drive; Johnson intercepting Miller to end another; Darryl Grant intercepting Miller to end another; and Coleman and Ravin Caldwell sacking Miller to end another.

Mayhew's fumble on a punt return set up a field goal, but with the Redskins leading, 31-30, Marshall got a sack to save the victory. The Redskins again shut off the run competely, holding the Falcons to four yards rushing in the second half.

The season ended with a 29-0 rout of the Seattle Seahawks. On Seattle's first four possessions of the second half, Stokes sacked Dave Krieg for a safety, Mann stripped the ball from Krieg, Coleman separated Bennie Blades from the ball and Davis intercepted Krieg. Yards rushing in the second half: Nine.

The Redskins ended last season believing they needed help at cornerback and on the defensive line, but they opened the season by shutting out the Cardinals. Again, they were dominant in the second half, with Phoenix's first four possessions resulting in: Mayhew's interception, Alvin Walton's interception return for a touchdown; Marshall's sack of Timm Rosenbach, and Bowles's pass deflection in the end zone.

The 49ers ran up 208 second-half yards against Washington in Candlestick Park on Sunday but they were held to two second-half field goals.

"We're playing well as a group," Mann said, "and that's the key to good defensive play. One person can't do it. That's just not the way it's done and as long as we continue thinking that way, good things will happen."