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Buddy Nix wasn't kidding when he identified improving the Buffalo Bills porous defense as being his top priority entering the NFL draft.

Once Auburn quarterback Cam Newton was out of the picture, the Bills general manager directed his attention in choosing defensive players with the team's first three picks — including both selections on Friday. After taking Texas cornerback Aaron Williams with the 34th pick, Buffalo drafted LSU linebacker Kelvin Sheppard at No. 68.

Add in Alabama defensive lineman Marcell Dareus, who was selected third overall on Thursday, and the Bills defense suddenly has a fresh new look. It was a unit that was undone by injuries, struggled in making the transition to the 3-4 system and finished last in the NFL in defending the run last season.

"It's obvious that we're not where we want to be defensively, and we're trying to fix that," Nix said. "And we're not through either."

Nix acknowledged the Bills changed course by concentrating on defense once Carolina selected Newton with the No. 1 pick. Though Missouri quarterback Blaine Gabbert was a possibility, the Bills went with Dareus at No. 3, believing he could make the best and most immediate impact on a team with numerous needs and coming off a 4-12 finish.

"With the first pick, we wanted a franchise (quarterback)," Nix said. "If he wasn't there, then we were going to get better on defense."

The 6-foot, 204-pound Williams is "an explosive hitter," who helped transform the Longhorns defense into one of the nation's best against the pass. He adds size to a comparatively small group of cornerbacks, and the Bills believe he also has the versatility to play safety.

"You have big receivers, and you so you need big corners, and they're hard to find," Nix said. "And this guy's talented."

In 37 career games, including 23 starts, Williams finished his career with four interceptions, six forced fumbles and 97 tackles.

He also provides depth to a unit that stands to lose veteran Drayton Florence to free agency this offseason.

Shortly after Williams was selected, Florence posted a message on his Twitter account essentially ruling out his return.

"Congrats Arron williams," Florence wrote. "I guess im done in buffalo enjoyed it while it lasted bills have the best fans!!!"

Sheppard, listed at 6-foot-2 and 250 pounds, led the Tigers in tackles in each of the past two seasons and is expected to provide help to a defense that allowed 200 yards rushing eight times last season. His 311 career tackles rank ninth in school history.

Bills coach Chan Gailey was impressed in seeing Sheppard firsthand at the Senior Bowl in January. Sheppard played for the South team that was coached by Gailey.

"He played sideline to sideline actually better in the Senior Bowl than he did sometimes on the tape," Gailey said. "We heard some good things about him, but we also heard there were some limitations about him. And we saw just the opposite."

Sheppard said he had an inkling the Bills might select him, especially after he traveled to Buffalo for a pre-draft visit.

"I kind of felt like I was coming back home," Sheppard said. "Once, I stepped into the door, everyone was like, 'Shepp, what's up, man?'"

From an overall perspective, Gailey regarded the first two days of the draft a success, because the Bills were able to address their defensive needs, even though they failed to land a potential franchise quarterback.

It helped that Gailey has confidence in journeyman quarterback Ryan Fitzpatrick, and the spark and cohesion he provided Buffalo's offense down the stretch last season.

"To me, Fitz's abilities, his leadership and the way he played last year gave us the freedom to be able to do what we needed to do with our football team," Gailey said.

The Bills have six picks over the final four rounds on Saturday, starting with the 100th selection.

Williams was elated once he was selected with the second pick of the second round.

"My emotions right now are crazy. I'm excited," Williams said. "I've got Marcell there, so we're going to try to bring as many wins as possible."

As it turns out, Williams is familiar with Dareus. Aside from the two spending offseasons working out together, they faced each other in the 2010 national championship game, in which Alabama beat Texas.

They also share a history of leveling big hits on big-name quarterbacks. Dareus' hit on Colt McCoy knocked out the Texas quarterback in the first quarter of the national championship. In October 2009, then-Oklahoma quarterback Sam Bradford re-injured his shoulder after being jerked down by Williams in a 16-13 win.

Williams then helped seal the victory with an acrobatic interception.