I think that may depend. The devil could always resort to real magic, but perhaps he has a weird love for trickery and skill as we mortals do.
There are many stories of the devil playing the fiddle, for example, when he could obviously create music without it (devil down in Georgia), or the bagpipes (Tam O'Shanter). The devil may be proud of his skill at sleight of hand, just as he is proud of his pickin' skills.
Just because he can use real magic doesn't mean he wouldn't enjoy sleight of hand and swindling for it's own sake.
Naturally, he might be tempted to cheat every now and then by resorting to real magic, especially when he is about to be bested.
A magic face-off would make most sense if it was true skill against skill--split fan productions, billiard balls, etc. This wouldn't be possible with two actors playing the roles.
A simplified routine with the cups and balls might make sense, with one sequence being done with the cups by the devil, and then the magician stepping up to the same set of cups and doing a fancier sequence.
Because of the supposed rivalry, it would be possible for each to set up for the other. That could be very interesting. When the magician wins, the devil could even become piqued and sit down to light a cigarette out of thin air by real magic--as Ray Walston did in Damn Yankees.
But I could even on a good day imagine the devil as a hobbiest, a very bad amateur magician who loves the cheap feather flowers, tubes and boxes of the magic shop and insists on showing them off every chance he gets.
He could demo the chinese sticks, square circle, phantom tube, temple screens, arm chopper, or any of several dozen magic shop classics.
He might well insist on demonstrating this kind of magic; stuff he has picked up on his regular visits to magic shops all over the planet. Come to think of it, I may have just had a whole new and very sobering vision of hell...