Historical Rules · 1 October 2009
Rule 103.2
Official source text from the 1 October 2009 Rules release
After the decks have been shuffled, the players determine which one of them will choose who takes the first turn. In an individual game, or in the first game of a match, the players may use any mutually agreeable method (flipping a coin, rolling dice, etc.) to do so. In a match of several games, the loser of the previous game chooses who takes the first turn. If the previous game was a draw, the player who made the choice in that game gets to make the choice in this game.