Though both bosses have heavy frost based powers, they also both have heavy frost resistance. That leaves their remaining abilities of which Kel'thuzad's Shadow Fissure was considered by commenters to be Sapphiron's downfall. The master claims victory over his guard.
The Archlich moves on to the final battle of the series next week to face off against the winner of tonight's titanic battle between the notorious scourge of the Outlands, Illidan Stormrage and possibly the most difficult boss in the game, the old god, C'thun. With only two weeks to go before we crown a winner, who will be the last boss to leave?