EAST RUTHERFORD, N.J. -- New York Giants rookie cornerback Will Peterson isn't good at keeping secrets.

Peterson spoiled coach Jim Fassel's attempt to keep Jason Sehorn's replacement at cornerback a secret by disclosing that he would start in Sunday's NFC East showdown in Philadelphia.

The disclosure wasn't much of a surprise in what is a must-win game for the Giants (7-7). If they lose, they miss the playoffs and the Eagles (9-5) win the NFC East.

After Sehorn, who is out with a sprained ankle, and fellow rookie Will Allen, Peterson has had the most playing time among the cornerbacks. He has three starts while playing in all the nickel and dime packages.

"I'm excited just to get another opportunity," Peterson said Wednesday. "Opportunities don't often come twice. I thought I would be the nickel going into the Philly game. Now getting an opportunity to start, it couldn't come at a better time with the situation we're in -- play well or go home."

This is a big game for Peterson for other reasons.

In the Eagles 10-9 win over the Giants on Oct. 22, Peterson was guarding James Thrash when Donovan McNabb rolled out and found the receiver for an 18-yard game-winning touchdown pass with 1:52 to play.

Peterson, who also started that game because Allen was sidelined with an ankle injury, watched a videotape of the play with the defense on Wednesday. He groaned like everyone else.

"I feel we did a good job the last time and had one breakdown," Peterson said. "You just want to get that off your chest. It's still there, but I don't dwell on it. It's not the focus of my season, or the focus of this game."

Peterson's coverage on the touchdown pass to Thrash wasn't bad. He fell a step behind as McNabb escaped the containment of the defensive line and found Thrash in the corner of the end zone.

"That wasn't his fault," Giants safety Sam Garnes said. "I don't think it was a bad play. He could have played it better, but they made a really great play. The ball was low and outside. Not too many guys could have made that throw. That was a great throw and catch."

Peterson, who has 43 tackles and an interception, said he is a better player now. He also said that play won't happen again this Sunday.

"In the NFL you just don't come in and play great as a cornerback," Peterson said. "You need some experience under your belt and to have some ups and downs, and I've done that."

Fassel, who refused to name a replacement for Sehorn on Wednesday, said Peterson is like most young cornerbacks. He's arrogant to a degree.

"One day you wake up and you say, `I belong,"' Fassel said of young cornerbacks.

Fassel had said after Sehorn's injury Sunday that he was considering veteran Dave Thomas as a possible replacement this week.

Thomas started the season opener at Denver, but only lasted a half. He had done little until Sunday when he made a late interception to ice the Giants win over Seattle.

However, Peterson said it's his job.

"I'm not thinking payback," he said. "I'm thinking of playing a great game."