[tardigrade]

I think maybe the most abstract definition would be to for each player take the total difference in EV between their play and FTOP play. If your overall delta EV is less negative than your opponent's, then you have outplayed him.

For instance, if you semi-bluff on the turn and your opponent folds a better hand, you have taken a small EV hit when compared to FTOP, but your opponent has taken a massive one.

Likewise, if your opponent draws against the odds and you don't pay him off when he hits, then you've outplayed him, etc.