Duke head coach Mike Krzyzewski’s genius insertion of Elliot Williams — a juicy McDonald’s Big Mac — into the starting lineup provided a boost for the slumping Blue Devils.

Meanwhile, UNC’s Wayne Ellington’s highs and lows seem to oscillate in sync with Carolina’s offensive success.

When Ellington’s hot, the Heels roll. When he’s not, well, it tends to be ugly, especially when Ellington tries to force 3-pointers down opponents’ throats.

Williams’ play mirrors what every coach dreams from a guard: size, strength, athleticism and length. The freshman’s ability to slash and dash by defenders adds another dimension to the spread offense Duke loves to run. Along with Gerald Henderson and Kyle Singler, Williams has shown the ability to make big jump shots in big moments and drive to the hole.

The freshman’s greatest impact has been on the defensive end. Against Florida State, Williams harassed Toney Douglas to the point where Douglas couldn’t even touch the ball on offense for several possessions near the end of the game. And when Douglas finally did get the ball, he forced several ill-advised 3-pointers.

William’s on-the-ball pressure against Ellington — and possibly Ty Lawson, depending on who Coach K matches him up with — might be the difference the Blue Devils need to right the ship against the Tar Heels.

The general trend in UNC’s past few victories has gone as follows: UNC gains lead around halftime, Duke rallies back and surges ahead and then UNC closes the game out by surging back and taking a commanding lead in the last few minutes.

If Williams can solve the Lawson problem that developed late in the second half of the February matchup, then it’s hard not to like the Blue Devils in this game.

Ellington, on the other hand, has the potential to go off at any time. Ellington made seven 3-pointers in the second half alone against Miami on Jan. 17.

The biggest issue for Ellington is allowing the game to come to him. Against the Yellow Jackets, the junior guard seemed to force shots once it was clear the offensive flow was going through Tyler Hansbrough and Deon Thompson.

Sometimes Ellington seems to get into a funk, thinking that he has to create his own shot to get going, but he tends to play best when he can find his shot in transition or after he hits a few jumpers early.

UNC fans tend to place a lot of the Tar Heels defensive lapses on Ellington’s shoulders — and, at times, Ellington can appear lost on defense. But he seems to be improving with a 4-16 shooting night by Virginia Tech guard Malcolm Delaney as the clearest evidence toward Ellington’s improvement on defense.

Ellington has yet to have a spectacular game against the Blue Devils. His freshman season he combined for seven points in two wins, and his shooting performance in the first game against Duke in 2008 was one of the biggest reasons why the Tar Heels lost.

His best game was a 16-point performance on 6-14 shooting in Cameron Indoor Stadium in 2008. If Ellington has a big night, the chances for the Blue Devils seem slim.

This is a tough one to pick. Williams’ play of late has been a huge boost for Duke, but this is his first significant role in a Duke-UNC game — not a good place for a freshman not named Tyler Hansbrough.

And Ellington seems to have healed from an arm injury and played exceptionally well against Virginia Tech. He also plays much better at home with all four of his games of 20 points or more coming in the Smith Center.

Advantage:

Sorry to be boring but neither team has an advantage here. Williams could just as easily play a huge role in a Duke victory as Ellington could torch the Blue Devils. If anything, Ellington’s experience would slightly tip the scales toward UNC. When it comes down to it, the two seem to offset each other pretty evenly, and I would put my money on other players being bigger factors in the outcome.

Disagree? Who would you give the advantage to?