PHILADELPHIA - Going back to the basics put Joe Gibbs and the Washington Redskins back in the playoffs.

Clinton Portis ran for 112 yards and two touchdowns, leading the Redskins to a hard-fought 31-20 victory over the woeful Philadelphia Eagles on Sunday.

Washington (10-6) clinched the NFL’s final playoff spot and its first postseason berth since 1999 with its fifth straight win. The victory also eliminated Dallas from contention.

“Looking back to 5-6, we talked at that time that if we lost another game we’d be out,” Gibbs said. “Trying to win five straight is a tough deal, but our guys seemed to understand what it would take. We went back to the basics.”

The Redskins play Tampa Bay (11-5) in an NFC wild-card game next Saturday in their first playoff game since losing 14-13 to the Buccaneers in a second-round matchup six years ago.

Just as it did against the Eagles, Washington relied heavily on its running game behind Portis and a strong defense to turn things around after losing three straight to fall to 5-6.

“The basics start with playing smart football, not turning it over and also running the football and playing solid defense,” quarterback Mark Brunell said. “That’s how you win. We’ve been doing those things. The first part of the year we weren’t.”

Mike McMahon threw two touchdown passes to Reggie Brown as Philadelphia (6-10) completed its first losing season since ’99 after reaching the Super Bowl last February.

“We’ll go back through and look at all of it,” coach Andy Reid said. “We’ve got to look at ourselves first, if we’re putting guys in the right position to make plays and did they make the plays.”

REDSKINS 17, BUCS 10      Who needs offense? 'Skins don't Washington rides defense to tight win WP: Defense delivers knockout punch Redskins’ Taylor ejected for spitting JT's Rant: Inexperienced QBs prove costly Mailbag: Sound off on first-round games Vote: Pick playoff winners Playoff matchups, schedules, predictions

McMahon, who struggled in his six starts for the injured Donovan McNabb, made a crucial mistake in the fourth quarter. His poorly thrown pass was tipped and intercepted by linebacker Lemar Marshall, putting the ball at the Eagles 22.

On the next play, Portis completely spun around to elude a tackle in the backfield, cut to the left and sprinted down the sideline into the end zone to give the Redskins a 24-20 lead.

“That play was designed to lose two yards,” Portis said. “I spun around a guy and it was clear from there.”