The Eagles jumped up three spots to select the Mississippi State defensive tackle with the No. 12 pick in the NFL draft on Thursday night.
"We thought he would be a top six or seven pick," coach Andy Reid said. "When he started to fall, we got excited about that. We had a price on how much we were willing to spend. Things were crazy. It worked out."
Cox, listed at 6-foot-4, 298 pounds, is a speedy, versatile lineman who can play inside or outside. He should fit right into Philadelphia's linemen rotation and bolster a run defense that allowed 142.3 yards per game last season.
"He'll be asked to play four, five plays and then the next guy comes in," Reid said. "He's one of those rare guys that size who can run as fast as he can."
Cox was named to the All-SEC first team after he collected 56 tackles and five sacks last season. He played three seasons at Mississippi State and had 114 tackles, including 24 1/2 for a loss, 8 1/2 sacks and blocked five kicks.
The Eagles sent their first-round pick (15th), a fourth (114th) and a sixth (172) to Seattle to get Cox.
"I was real excited," Cox said. "It's a defensive scheme I would like to play in and it'll be a pleasure to play under coach Washburn."
This is the fifth time in Reid's 14 seasons as head coach that Philadelphia chose a defensive lineman in the first round and the third time they took a tackle. The Eagles selected Mike Patterson (31st) and Brodrick Bunkley (14th) in consecutive years in 2005-06, and took Corey Simon at No. 6 in 2000.
"You win games up front whether it's the offensive or defensive line," Reid said. "If you can perform up front, you make everybody else better."
The Eagles are coming off a disappointing 8-8 season that began with Super Bowl aspirations. Injuries and a mediocre defense were the biggest problems. They already improved a weak linebacker corps by trading for two-time Pro Bowl pick DeMeco Ryans. Now they've added a potential impact player to help disrupt quarterbacks.
"I'm a guy with a great attitude, hard-working who loves to compete," Cox said. "I play at 100 miles per hour. That's what I like to do."
Reid was sold on Cox after Washburn spent a day with him in Starkville, Miss.
"He was so quick to learn," Reid said. "You're looking at a kid who is talented, who's intelligent and his athletic ability jumped out at you."