DURHAM - Duke guard DeMarcus Nelson had the roughest game of his senior season in Duke's home loss to North Carolina on Saturday.

So when Duke (26-4) meets the Georgia Tech-Virginia winner at 7 p.m. Friday in the ACC Tournament in Charlotte, look for Nelson to go to his calling card -- defense -- to get himself and his basketball team back on track.

Since arriving at Duke in 2004, Nelson has done that after starting slowly or when his team needs a boost.

Because this Duke team, which is trying to earn a No. 1 seed in the NCAA Tournament, wants to turn defense into offense, forcing turnovers and scoring on the other end -- and because Duke has the depth to play fast on both ends -- Nelson has been a great weapon this season.

Nelson, who was chosen to the all-ACC first team and ACC all-defensive team Monday, is a strong candidate for the ACC defensive player of the year award. After all, Nelson is the guy who has guarded and caused trouble for fellow ACC first-teamers Sean Singletary (Virginia), Tyrese Rice (Boston College) and Jack McClinton (Miami) in his career.

Duke coach Mike Krzyzewski said Nelson has been an asset since he arrived and keyed Duke's defensive strategy the past two seasons. At 6 feet 4, Nelson can guard four of five positions on the floor.

When Duke beat a frontcourt-laden Oklahoma in December 2004, the freshman Nelson guarded big men Kevin Bookout and Taj Gray, holding Gray to six second-half points while Duke's Shavlik Randolph was in foul trouble.

A deep reserve of confidence helps Nelson, who was chosen a finalist for the John Wooden national player of the year award Monday -- forget the few times when he gets beat.

Asked which player he's locked down best during his career, and Nelson said, "Um, I think I got everybody's number, honestly.

"When we go into a game, I feel I can contain any guy and make him take tough shots. That's how I look at it."

Nelson is physically strong with broad shoulders and 200 pounds of muscle packed on his frame. But a misleading body allows him to play bigger than his size.

Nelson is bowlegged and has a slight case of scoliosis, or curvature, in his back. If you straightened him out, he'd probably stand 6-6. That explains the 7-foot wingspan that allows him to tip away passes, block shots on taller players, and get his fingers on rebounds.

"You go against him and you get a little space and you think you have a shot, and he blocks it," teammate Jon Scheyer said.

This season, Krzyzewski has put Nelson on a key perimeter player but often switched him to the hot hand when necessary.

In a win over N.C. State on March 1, Nelson started on 6-5 guard Courtney Fells, switched to 6-8 forward Gavin Grant and spent time trying to slow 6-0 point guard Javier Gonzalez in the midst of a 19-point performance. He switched between Wayne Ellington and Ty Lawson against UNC.

"It gets wild," Nelson said.

Duke has played strong defense this season on the perimeter, denying passing lanes to force turnovers, because Scheyer, Gerald Henderson and Greg Paulus have improved as defenders.

Still, all the switching that Nelson does hasn't gone unnoticed by his teammates.

"[Opponents] have more confidence if they don't see DeMarcus guarding them," Scheyer said. "If I was on the opposing team, I wouldn't want him guarding me."

Nelson said the toughest assignments he's had have been against teammate and ACC career scoring leader J.J. Redick in practice, and lightning-quick guards like North Carolina's Raymond Felton, Virginia's Singletary and Boston College's Rice.

"For me, when I go against those small guys, that's when I'm most concerned," Nelson said. "They're quicker, and they can get into creases easier.

"What I've learned to do better is get into good shape, contain whoever the best perimeter player is, then go on the offensive end and still be very productive."