SEATTLE — The only thing questionable about Clinton Portis is why he even bothers to practice.

Washington’s star running back darted and pounded for 143 yards on 29 carries, including key ones late that helped preserve the Redskins’ first victory in almost a month, 20-17 over the Seattle Seahawks on Sunday.

Portis was questionable to play after missing most of practice thi

s week because of his sprained knee. Then, the NFL’s leader in yards from scrimmage injured a muscle near his hip late in the first half, when he rushed for 69 of his yards.

Yet he kept running, finishing with his first 100-yard day since the Redskins’ las

t win, on Oct. 26 at Detroit, and ending a two-game losing streak for Washington (7-4).

The Redskins didn’t stay tied with Dallas for second place in the NFC East until Seattle’s Matt Hasselbeck flicked a horridly underthrown pass that former Seahawk Shawn

Springs intercepted near midfield with 1:20 left. That was one play after Ladell Betts, who earlier ran for a touchdown, lost a fumble deep in Seattle territory.

Hasselbeck simply pounded his thigh pads in frustration as Seattle sunk to 2-9, its worst sta

rt since 1992.

The Seahawks lost for the fourth straight time at home. That last happened to the 2-14 team of 1992. Seattle had been an NFC-best 42-14 at home since 2001 entering this season.

The Redskins were pinned by a downed punt at their own 4 with se

ven minutes left while leading 20-17. Portis then ripped off darting runs of nine, 11 and 20 yards, leading Washington into Seahawks territory and all but clinching the win until Betts’ fumble nearly blew it.

Springs’ interceptions ensured coach Jim Zorn w

as a winner in the return of the former Seahawks quarterback and assistant coach.

The decisive score came after Jason Campbell, who was 20 of 33 for 206 yards and a touchdown, found Santana Moss alone in the flat on third-and-5 from the Redskins 49 early i

n the fourth quarter and Moss ran through Lofa Tatupu’s tackle attempt for a 24-yard gain to the Seahawks 27. That set up the second field goal of the game by Shaun Suisham, from 22 yards, and Washington led 20-17 with 9:19 left.

A still-rusty and rattled-

looking Hasselbeck completed 12 of 24 passes for just 103 yards. It was his first two-touchdown passing day since last Dec. 23 against Baltimore.