Yes, this works. I know some Modern decks use this as a win condition.
October 9, 2014 3:47 p.m.
Your opponent loses the game. As far as I know thats from a rules point of view not exactly the same as you winning the game but it has the same result. Also Pacts require a player to pay mana at the beginning of his upkeep wich is not an upkeep cost. Only cards with cumulative upkeep like Mystic Remora have an actual upkeep cost.
October 9, 2014 3:51 p.m.
@magicnerd0815: "Upkeep cost" is a colloquial term for any costs that must be paid during an upkeep step. These costs don't necessarily have to be cumulative upkeep costs.