With me being nightelf and having a slight stealthing advantage, this comp is fairly easy most of the time. It's all about finding the opposing rogue, and letting your mage duel the priest in the meantime. If you don't find the opposing rogue (Or he doesn't find you) instantly, you should apply a sap to the priest and have your mage start spellstealing him. If by some miracle you happen to land all your spell steals (it never happens, honestly) and have the priest stripped of all his buffs, it might be a good idea to surprise him by starting with a Cheap Shot, Mutilate, Eviscerate, Vanish and let your mage nuke him low or sometimes even dead. At this point you must have achieved at least a trinket or a Pain Suppression. Take into account that this RARELY works though. 90% of the matches one rogue finds the other, and the match begins from there. There are two scenarios once again.
A) You find the opposing rogue
B) He finds you

A) At this point have your mage spell steal the rogue a couple of times, with a hint of luck you might be able to dispel a shield or fortitude. Start off with a cheap shot (NOT garrote, never ever) and have your mage PoM-Polymorph the priest and keep an eye on the rogue's trinket-readiness. If he does not wish to trinket, continue with a full duration Kidney Shot and tear his arse to oblivion. Game won. If, however he trinkets the stun, you will probably get blinded (Always have evasion up after every cheap shot to win 25% of the matches instantly). Do not hassle, because this is nothing to worry about. Usually you will get opened on with either a garrote or a cheapshot, it doesn't matter much. Insta-trinket any incoming stun and blind the opposing rogue, make sure your mage does NOT dps him at this point. After the full duration blind, try to land a sap on the rogue in order to gain access to full-duration stuns for the second opener. If the priest tries to holynova around the rogue, have your mage polymorph him in between global cooldowns. The rogue will NEVER survive a full duration stun with your Mage blowing off cooldowns. And I mean NEVAR!

B) This is usually pretty messy, but still beatable. Your mage should start spamming AoE always when you get sapped in order to find the nearby rogue. Never trinket anything other than the opposing rogue's Cheap Shot opener, and always insta-blind him right after trinketing. Your goal here is of course to get the other rogue to blow his trinket, and if he catches you in stun without your trinket, there is no surviving that. I doubt that any of the high rated rogues will trinket the initial blind, and therefore after opening with cheap shot, you must instantly blow all your cooldowns and counterspell the priest in order to get the kill, simply because you have already used your trinket and are vulnerable to any incoming stuns / fears. If you fail this initial burst, you might have a chance at resetting the match, but I wouldn't count on it.