Redskins offensive guard Kory Lichtensteiger reacts after a loss to the Cowboys. The offensive line played well for much of the night but fell victim to huge plays late. (Toni L. Sandys/WASHINGTON POST)

Through three quarters Monday night, the Washington Redskins’ offensive line — long a source of frustration, seemingly an annual question mark coming out of training camp — had done just about everything asked of it against the Dallas Cowboys. Quarterback Rex Grossman had enough time. The Redskins moved the ball regularly.

And then, with the game in the balance, it all changed.

Washington’s 18-16 loss will be remembered for a huge third-and-21 conversion by Dallas, and by Dallas place kicker Dan Bailey’s six field goals. But when the Redskins had a chance to win the game, twice, by protecting Grossman, the offensive line didn’t answer.

“We expected to go out there and get it done, and win,” tackle Trent Williams said. “And when we had to, it didn’t happen.”

When the Redskins got the ball with 6 minutes 53 seconds remaining, they held a tenuous 16-15 lead.

They moved into Dallas territory after Grossman hit Santana Moss on a six-yard pass play and tacked on 15 more yards for an illegal hit by safety Alan Ball. They were moving the ball. Grossman had time.

Dallas outside linebacker DeMarcus Ware — a Washington terror in the past, with three sacks and 12 tackles in the two meetings between the teams a year ago — had been relatively quiet.

“Overall, they did a great job,” Grossman said. “I felt like I had plenty of time to go through my reads. That’s all you can ask for.”

But on second down, Ware — who new Cowboys defensive coordinator Rob Ryan moves all over the field — got matched up with Redskins right tackle Jammal Brown. Brown, who had done a fine job all night, finally was beaten, and beaten badly. Ware simply ran around him, and his sack pushed the Redskins to third and 17.

On the next play, Ware beat Williams to pressure Grossman, and the Redskins — with a chance to win — had to punt.

Still, the Redskins got another chance, taking the ball at their own 20 with 1:47 remaining. Immediately, Brown was whistled for a false start, making the task more difficult.

Grossman managed completions to running back Tim Hightower and wide receiver Jabar Gaffney, moving the ball to the 43. One more big play — even with the clock near 30 seconds — could have set Washington up for a winning field goal attempt from Graham Gano.

On second and 10, Grossman dropped back. Anthony Spencer, the linebacker opposite Ware, found himself on Brown. Spencer ran around him.

“I went to my left and felt some pressure,” Grossman said.

So he ran further left. “You try to find a soft spot and make a play,” Grossman said. But Spencer — with Brown long behind him — made the play first. He crushed Grossman from behind, forcing a fumble that the Cowboys recovered.

What happened?

“I don’t know, man,” Brown said. “I don’t know.”

What happened was the life of an offensive lineman: Instead of being remembered for a night of solid play, Brown and his mates will remember those final two drives. Afterward, Brown sat at his locker in full uniform, staring blankly. He turned to Williams: “What happened on that last play?”

On a night in which the offensive line held up for so long, that was the lingering question.