Pwnage isn't just losing a fight. These are situations where one opponent significantly outclasses the other to the point of embarrassment.
Qualifications
For the pwner, the battle usually involves a few of these things:
one-hit KO
flawless victories
not breaking a sweat
a lack of focus/interest in the fight
never using your high level attacks
being outnumbered but shrugging it off like, "meh"
decimation of your opponent after analyzing their abilities
not avoiding your enemies strongest attack and sustaining no injury outside of dirtied clothes, if that
letting your fists explain why your smack talk was an act of mercy, not conceit, and that the opponent should have listened to you
For the pwnee, the battle usually involves selections from the following:
planning and preparation
breaking out your best strategies and attacks
knowing that nobody could possibly be that strong
pouring your heart into a battle with everything on the line
Important Questions
If a person takes severe injuries or is beaten to a pulp, but still wins, can pwnage occur?
Although rare, a pwner can receive serious injuries during a battle and still pwn.
An injured Mustang re-enters the fight..
For example, in FullMetal Alchemist: Brotherhood Episode #19, Roy Mustang is battling against an opponent namedLust who by all accounts should have outclassed him. Mustang received a pretty brutal thrashing from Lust and a serious injury as well. However, the battle didn't end with that.
... chumps his opponent off with some smack talk...
Roy Mustang was able to heal himself, analyze his opponent and counter attack. Mustang spoke confidently that he had figured out her attack and knew how to kill her. After the first of his many assaults, Lust's attitude had changed to fear and rage at the fact that Mustang had indeed figured out her weakness and that she was going to die beyond any shadow of a doubt. It can be said that at this point, the tide of battle turned in a severely lopsided way and Mustang began to pwn his opponent.
... and begins his pwnage.
So yes, while rare, a person can sustain serious injury but still pwn their opponent. Some of the usual traits of these situations are battles where one person has an unpredictable ability that will give them an upper hand until their opponent is aware that they have said ability.