It’s difficult to imagine the Washington Redskins’ offensive unit that opened Sunday’s game against the New York Jets was the same one that finished it. The first-quarter version was polished and poised, never so much as facing a third down before it reached the end zone. The second-half version was a mess, failing to gain a first down on six of nine possessions, turning it over twice, never reaching the red zone, never mind the end zone.

“The first half was all right,” quarterback Rex Grossman said. “The second half, it was always something.”

The combination of those two disparate halves resulted in a 34-19 loss that might well have been a win had the second-half offense even slightly resembled its distant cousin from the first half. The Redskins had one first-quarter possession, used it to gain 82 yards and score a touchdown, and couldn’t have looked — or felt — much better. They had four third-quarter possessions, gained a total of 11 yards on them, punted three times and fumbled on the other, and couldn’t have looked — or felt — much worse.

“For whatever reason, we lost — I wouldn’t say we lost our poise — but they got the job done and we didn’t,” Coach Mike Shanahan said. “I thought we took it to them in the first quarter and a half. We had the momentum going, and all of a sudden it didn’t seem like we could get anything going.”

Before last week’s victory over Seattle, the Redskins hadn’t scored a single touchdown on their game-opening possessions. Sunday, they did so for the second straight week with what might have been their best drive of the year. It began with a 15-yard run from rookie running back Roy Helu. It opened up with a 42-yard pass from Grossman to tight end Fred Davis that pushed the ball to the Jets’ 14-yard line. And it finished with three runs from Helu, the last a touchdown from two yards out.

The drive was so efficient, the Redskins ran eight plays and only faced second down three times. It came completely off the 16-play script offensive coordinator Kyle Shanahan writes to open the game — a plan that can be thrown off-kilter when third downs arise.

“We were able to score, which obviously feels good on the first drive,” Grossman said. “But that was the only touchdown of the game — pretty much the reason why we lost.”

What happened from there on out looked eerily like the Redskins’ offense during its three-week hiatus, games against Buffalo, San Francisco and Miami that yielded just one touchdown total. Helu had 63 yards rushing at halftime; just 37 thereafter. Davis had four catches for 82 yards in the first half; two for 19 after that. Grossman was 10 for 26 with an interception, a fumble and two sacks in the second half. The entire operation seemed to shut down.

“We came out, we drove right down the field,” wide receiver Donte Stallworth said. “We ran the ball well. And pretty much after the first quarter, things got shaky.”

Shanahan said the Jets began the game using mostly zone coverage, and then shifted their talented defensive backfield to more man-to-man. The Redskins did not adjust back. Their initial first down of the second half came on their fifth possession — and not until the fourth quarter.

“On offense, we had a chance to get the momentum of the game, and we didn’t,” Mike Shanahan said. “I’m just disappointed in the way we finished. We didn’t get much going on offense.”

On offense,a tale oftwo halves

In the first half of Sunday’s game, the Redskins tallied 13 first downs and 183 net yards (105 of those came in the first quarter alone).

In the second half, that dwindled to six first downs and 121 net yards. The third quarter was particularly dismal, with 11 net yards on 12 offensive plays for zero first downs.