Triple R
Smash Lord
While I'm sure your opponent knows about DI, he didn't DI in that instant to avoid hitting the ground so early, but that's beside the point. I'm pretty sure you had enough time to just do a jab lock to him. For future reference, trying bairing them and then dashing towards them. Then use your shield to stop, then jab lock them.I did it today in a small online tournament. My opponent was a spammy toon link but he knew DI, SDI and stuff.
http://www.youtube.com/watch?v=z_3eiFZjFnI
As you can see his room to airdodge wasn't that big. That's not meant to be used every match, but if one day your opponent misses a tech...