ORCHARD PARK, N.Y. (AP) -Ko Simpson was already motivated when the Buffalo Bills selected him, though he was unhappy he had to wait until Day 2 of the NFL draft.

``I came in here with a chip that I should've been picked much higher,'' the South Carolina native said after practice Thursday, as the Bills (7-8) prepared for their season finale at Baltimore this weekend. ``I was disappointed that I went in the fourth round.''

Little did the rookie free safety know how quickly he'd have an opportunity to show he was a capable NFL player. From fourth-round pick to regular starter, Simpson's done plenty to prove wrong the 31 teams that overlooked him in April.

``I feel like I got thrown into a good situation,'' Simpson said.

'Thrown in' is an apt description for a player who figured he'd spend this season stuck mostly on special teams and tutoring behind veteran starter Troy Vincent.

Simpson was thrust into a starting role in the first quarter of the Bills' season-opener at New England after Vincent hurt his hamstring. The injury placed Vincent on injured reserve and led to his release.

With no other free safety on their depth chart, the Bills put their faith in Simpson despite his mere two years of college playing time.

He's delivered, joining first-round pick Donte Whitner as part of Buffalo's two-rookie safety tandem that has solidified the team's defensive backfield.

``They've done a real nice job,'' coach Dick Jauron said. ``We thought Ko would have a little bit of time to gain some comfort, but it didn't work out that way. ... It turns out it should be good for them in the long run.''

Whitner has generated most of the attention, enjoying a solid season and tying for second on the team with 95 tackles.

Meanwhile, Simpson has emerged as a steady player. He's become part of a Bills unit that, despite its struggles against the run this season, is only one of five NFL defenses that hasn't allowed an opponent 300 yards passing.

Simpson's 86 tackles rank fifth on the team. He has two interceptions, including a tipped Brett Favre pass he caught in the end zone and returned 76 yards to seal a 24-10 win over Green Bay on Nov. 5. He's also registered a sack and a forced fumble.

``Troy told me he was going to take me under his wing. But after he left, I was like on my own,'' Simpson said. ``I've been learning on the run.''

The knock against Simpson entering the draft was that he might be too inexperienced, even though he had two solid seasons with the Gamecocks. He was named the SEC's freshman of the year in 2004 and was a consensus SEC first-team selection last season, when he led conference defensive backs with 103 tackles.

Simpson has showed range in playing the Bills' Cover 2 defensive scheme, which mostly requires the free safety to ensure no opposing receiver gets behind him. And he's not averse to contact, providing support against the run.

Simpson and Whitner have another thing in common going back to draft day.

Besides Simpson's belief that he was selected too low, Whitner has faced questions of whether the Bills chose him too high with the eighth overall pick.

Funny, how things turned out.

``Both of us came in here trying to prove that we belong,'' Simpson said. ``I think we're doing very well.''

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