Yasuo vs Karthus

Recently I've been spamming in Dominion, and got to face a few times.

Maybe they just happened to be bad, but It surprised me to discover just how powerful is 1v1 vs .

could not damage me without stepping on Defile, which hurts. He could dodge the first few Qs, but Defile made short work of any minion he could dash to, and W made sure he'd eat all the next Qs. (For those who don't know, a Karthus' W cancels 15% of the enemy's MR and, when maxed, has a 5 seconds decaying slow that starts at 80%)

His WindWall blocked none of my skills.

Even if he did manage to Q-Ult me, he'd have to eat Defile ticks through all the time, and a return kill was pretty much guarenteed whenever he did manage to kill me; this is without even considering that he could never end up with less than 60% HP after a fight with anyone else, or I'd just ult and get the kill. Hell, if I ulted during an 1v1 of him vs anyone else he'd lose it automatically.

Since Dominion is mostly about early/mid game, which is 's weak point, I was wondering: how strong is him vs Yasuo on Summoners' Rift?

ChampionSelect.net does not list Karthus as neither a counter nor as countered by Yasuou though...