The Eagles needed just a couple of inches for a fourth-down conversion and couldn't get it.

The Dallas Cowboys needed 14 yards on a third-down play a few moments later and they got a lot more that just a first down.

Those two plays proved pivotal in the Cowboys' 20-16 victory last night at Lincoln Financial Field, allowing Dallas to leave Philadelphia atop the NFC East.

The Cowboys improved to 6-2 halfway through the regular season while the Eagles slipped to 5-3.

With the score tied at 13 and just over 11 minutes remaining in the game, Eagles quarterback Donovan McNabb tried to pick up the few inches needed for a first down by running a sneak.

Side judge Rick Patterson decided McNabb came up short of the first-down marker. Eagles coach Andy Reid challenged the decision with a red flag, but referee Walt Coleman, after going under the replay hood on the home team's sideline, ruled that Patterson's spot was correct.

That gave Dallas the football at its own 45-yard line, and four plays later, quarterback Tony Romo was faced with a third-and-14 situation at the Eagles' 49-yard line.

Romo got cornerback Sheldon Brown to bite on a pump fake that left receiver Miles Austin open for a 49-yard touchdown. It was Austin's only catch of the evening.

Reid's failed challenge was his second of the game and it also left the Eagles without any time-outs. That proved costly at the end of the game.

After David Akers connected on a 52-yard field goal with 4 minutes, 27 seconds remaining in the game to cut the Cowboys' lead to four points, Dallas managed to convert a couple of first downs and the Eagles watched helplessly as Romo knelt down three times to run out the clock.

Another failed opportunity in a short-yardage situation during the third quarter also proved costly to the Eagles.

Reid lost a challenge and a time-out on a pass from McNabb to rookie running back LeSean McCoy, leaving the team in a fourth-and-inches situation from their own 42-yard line.

The coach opted to go on fourth down, but tackle Jason Peters was flagged for a false start when his left leg slightly flinched. The Eagles punted.

Dallas' first seven points came courtesy of a short field provided by rookie receiver Jeremy Maclin when he let a McNabb pass slip through his hands. Cowboys safety Gerald Sensabaugh benefited from the rookie mistake with an interception at the Philadelphia 37-yard line.

Despite a holding penalty that immediately backed Dallas to the 47-yard line, Romo led the Cowboys on a seven-play touchdown drive, converting a third-and-6 play with a 9-yard pass to tight end Jason Witten and a third-and-9 with a 21-yard pop screen to rookie receiver Kevin Ogletree.

Tashard Choice, after lining up in the Wildcat formation, covered the final 2 yards for the score.

The Eagles countered with two second-quarter field goals from 45 and 48 yards by Akers, but spent most of the first half struggling badly in the passing game. McNabb completed just six of 14 passes for 88 yards in the first half. He was also sacked three times as the Eagles had to juggle their offensive line after Peters suffered an ankle injury with 3:47 left in the first quarter.

With Peters on the sideline, the Eagles moved Todd Herremans from left guard to left tackle, Nick Cole from right guard to left guard and inserted Stacy Andrews at right guard.

Leading receiver DeSean Jackson also struggled in the first half as he failed to catch a pass against a Dallas defense that continually rolled coverage in his direction.

McCoy and fullback Leonard Weaver proved to be the most effective method of offense in the first half. The two combined for 68 yards on just 12 carries. A 17-yard run by McCoy set up Akers' first field goal, and the running game accounted for 41 of the 54 yards that led to Akers' 48-yard field goal with 1:38 left in the half.

The Cowboys, thanks to a 64-yard pass from Romo to Patrick Crayton, got three points back just before halftime on a short field goal by Nick Folk.

It appeared as if the Eagles had taken their first lead of the night at the start of the second half when returner Ellis Hobbs returned a kickoff 96 yards for a touchdown, but a holding penalty on rookie Moise Fokou negated that big play.

A series of big plays followed as the Eagles put together their best offensive drive of the night. McNabb completed four of five passes for 73 yards, including a 45-yard connection to McCoy that went all the way to the Dallas 15-yard line.

Two plays later, McNabb avoided heavy pressure and threw an 11-yard touchdown pass to tight end Brent Celek, giving the Eagles their first lead of the night at 13-10.

Late in the third quarter, cornerback Michael Jenkins intercepted a McNabb pass at the 45-yard line. Maclin grabbed Jenkins' face mask as the cornerback went to the ground, and the 15-yard penalty gave Dallas the ball in Eagles territory.

It was the Cowboys and Romo who came through with the big plays in the final quarter.

Contact staff writer Bob Brookover at 215-854-2577 or bbrookover@phillynews.com.