I can't remember finding the same legendary in short succession in the same game, but I have noticed that I tend to get multiple legendaries in the same game. I'll do maybe 6-8 runs through Act 3 per lvl and find maybe 2-3 legendaries along the way and they're all from the same game.

I find legendaries in pairs so often I can't help but think this isn't coincidence and there is some hidden algorithm in the background that effects your drop chances when a game is created.