ALAMEDA, Calif. (AP) -- Less than three years after being one of the most prized free agents on the open market, Nnamdi Asomugha' NFL career is over.
Asomugha formally announced his retirement Friday at the Oakland Raiders' headquarters, ending his 11-year career at the place he had his most success.
''I'm just grateful to be back, grateful for everything to go full circle,'' Asomugha said. ''For all of the achievements and awards, to be able to retire as a Raider ranks highest among all of those.''
Asomugha made three Pro Bowls and was a two-time first-team All-Pro during his eight seasons with the Raiders when he was considered one of the league's top cover cornerbacks.
But his career quickly fizzled after signing a $60 million, five-year contract with Philadelphia in the summer of 2011. He was cut after two years with the Eagles and played just three games this season for San Francisco before being released in November.
He said he had opportunities to come back since then but felt the time was right to go on with the rest of his life.
Asomugha was joined at his retirement news conference by three of the Raiders' best defensive backs: Hall of Famer Willie Brown, Lester Hayes and Charles Woodson. Asomugha credited all three, along with others like Rod Woodson and Mike Haynes for his transformation from a college safety to an elite NFL cornerback.
''He turned into what they call that shut-down corner,'' Woodson said. ''People just decided going into the game they weren't going to throw at him. That's a testament to his hard work.''
Asomugha came into the NFL as a first-round pick out of California in 2003 and became one of the rare Al Davis first-rounders to pan out in his later years running the Raiders.
After taking a few years to adjust to playing cornerback after being mostly a safety in college, Asomugha thrived in the Raiders' system that often left cornerbacks alone on an island matched up man-to-man against opposing receivers.
''When I first came into the league not too many people really knew who I was,'' Asomugha said. ''When I first got here I was definitely called a reach. In great Al Davis fashion, he took a reach that he believed in and instilled confidence in me like nobody else could and I was able to become all that he expected of me.''
Asomugha had a breakthrough season in 2006 when he intercepted eight passes and was a rare bright spot on a 2-14 team. By the next season, opposing quarterbacks rarely even threw the ball his direction.
In his final four seasons with the Raiders, Asomugha had just 136 passes thrown at him in 60 games, allowing just 66 completions and only two touchdowns.
Asomugha was paid well for his performance in Oakland, earning $9.5 million in 2008 and then signing a $45.3 million, three-year deal the following offseason. That contract voided after his second year and he became one of the most prominent free agents after the lockout ended in 2011.
After never playing on a winning team in his eight seasons in Oakland, Asomugha joined the Eagles in what was billed as the ''dream team.'' But he never fit in to a system that had him playing zone coverage instead of being exclusively in man-to-man.
Philadelphia was one of the league's most disappointing teams in his two seasons there, going 12-20 and missing the playoffs both times.
Asomugha signed a minimum contract with the 49ers last offseason but made one start and played three games before being released, meaning he will end his career having never made the playoffs.
''We didn't get a championship, that was the goal,'' Asomugha said. ''But we had a lot of championship moments here and that's the stuff I can be proud of moving forward.''