Bet you can't get enough of Mega Man in Super Smash Bros, so here's some more! In this IGN video we see a demonstration of Mega Man in a one-on-one fight against Mario that goes all the way to the wire. And I don't know who is giving the play-by-play but I want him to be my friend.
Also of note, Mega Man appears to use a move yet unannounced at the very end of the fight (before sudden death). It appears to perhaps be Mega Man 2's Air Shooter or Mega Man 6's Wind Storm. Or perhaps it's just a variation on Top Spin. We'll get to know eventually, as I'm sure there will be plenty more footage and details down the road. You can also see this footage but with more of a lead-in here.
Thanks for the tip, Magnet_Man!
Update: Changed the video to a fuller, much clearer version of the same fight, courtesy of GameTrailers. --LBD