New England Patriots quarterback Matt Cassel put an exclamation point on his reversal of fortune last week.

By the fourth quarter of the Pats' rout of Arizona, Cassel had called it a day after putting up 345 passing yards and staking New England to a 47-0 lead.

At that point he stood on the sideline and watched the man who kept him on the bench for two years in college, Matt Leinart, perform mop-up duty as the backup QB for the Cardinals.

How times have changed for Cassel.

"It is pretty ironic because there were a lot of days when I was doing that, and he was the one sitting on the sideline," Cassel said, referring to his days at the University of Southern California. "He got the big lead, and I got to go in late in the fourth quarter and do some stuff. ... It is pretty crazy."

Bench-warmers everywhere can revel in the Cassel fairy tale. He's a guy who spent four years in college sitting behind not one, but two Heisman Trophy winners — Leinart and Carson Palmer. He attempted only 33 passes in five years at Southern Cal. He went eight seasons between starts — from the last game of his high school career in 1999 to the second game of this season for the Patriots, after Tom Brady went down with a knee injury.

It turns out it was worth the wait. Cassel comes to Buffalo on Sunday to face the Bills, having helped the Patriots to a 10-5 record.

He directs the fourth-ranked offense in the NFL. He ranks eighth in the NFL in passing yards (3,615), 11th in completion percentage (63.2) and 11th in passer rating (89.1).

"I think the two most important things for any quarterback is decision making and accuracy," said Patriots coach Bill Belichick. "You can't be a good quarterback without those two elements, and I think Matt has displayed those throughout the course of the year."

"You never really know what you're capable of until you get in there and you actually do it," Cassel said. "I always had a strong belief in myself that I could go out there and execute the offense and win ballgames. But until you actually go out there and do it, you don't really know. I guess I have exceeded my own expectations."

Cassel never expected to be drafted when he came out of USC in 2005. The Patriots took him in the seventh round. He was the 13th quarterback picked.

"To be completely honest, I didn't think I would get drafted because of the lack of playing time in college," he said.

The Patriots saw a guy with ideal size (6-foot-4 and 230 pounds) and a decent arm who was good enough to get recruited to one of the top programs in the country.

"There wasn't much to go on," Belichick admitted this week on a conference call with Buffalo media. "I'd say the big things for us were his workout, which was good. He showed all the physical skills that he has passing and athletically and all that. Then our conversations with him where we could get a little bit of a sense of his maturity, his intelligence level and overall football understanding."

"A very big part of that was the recommendation from Pete Carroll from USC of how competitive he was with Leinart and Carson Palmer and all that. All that being said, Matt's come a long way in four years, and he's come a long way this year with the opportunity to play and how much he's learned and gained from each of those opportunities."

The Patriots' confidence in Cassel has grown. In his second start, a 38-13 loss to Miami, he was on a short leash, completing 19 of 31 passes for 131 yards. Nine weeks later in a 48-28 rout of Miami, Cassel operated out of the spread formation almost the whole game and hit 30 of 43 passes for 415 yards.

"The first time we played Miami to the second time we played Miami was a great example of how far along we came from early on in the season to now," Cassel said. "I've been here for four years. I knew the offense all along. It was just I think the coaching staff didn't know how I was going to respond. ... They built confidence and put more plays in the playbook, expanded it and put more responsibility on my shoulders."

Cassel became just the fifth NFL quarterback ever to post back-to-back 400-yard passing games, doing it against the Jets and Miami. The Patriots have cracked the 40-point mark four times, including the last two weeks heading into Sunday's game against the Bills.

"He throws the ball extremely well," said Bills defensive coordinator Perry Fewell. "He's not running as much as he did before, but he still can escape and has the ability to run. He's distributing the ball to more people. It seems as though before he was distributing the ball to Wes [Welker] and to his backs, but he's going more to Randy [Moss] and he's using all of his weapons now."

Cassel is thankful for his situation. He has a great cast of weapons, including Moss, who caught an NFL-record 23 TD passes last year, and Welker, who leads the NFL in catches this year with 109. Of course, he also has great coaching from Belichick and the Pats' staff.

"Those guys definitely make any quarterback's job a lot easier because of their God-given talent and their physical abilities," Cassel said. "We've got a great cast of characters, from the running backs to the receivers to the offensive linemen. It just makes it a lot easier day usually for me."

How much of Cassel's success is a result of his great weapons and winning system? That's what NFL general managers must decide this offseason, because Cassel is a free agent, and is likely to strike it rich.

It would seem that he would be best suited to a West Coast offense that puts a high priority on accuracy and short to intermediate passing. The Patriots probably will make him a good offer to stay as Brady's backup. But he's very likely to get a better offer to be a starter.

"Nobody knows the future," Cassel said. "If anybody knew the future, I probably wouldn't be here right now, with a lot of people predicting that I wouldn't be here after the preseason. The fact is, nobody knows where I'm going to be next year and I could definitely be back here. But it's something that we're going to have to wait and see."