This was the 1st series contested by the new National Hockey League - NHL - As with the three previous NHA-PCHA Cup Final series, the series alternated between the NHL champion and the PCHA champion each year, while the differing rules for the leagues alternated each game. This meant that all of the games for the 1918 championship series were played at Toronto's Arena Gardens. Two of the major differences between the two leagues' rules proved to be a major factor in the series. The PCHA did not allow forward passing and played with seven players per side; the NHL did not adopt forward passing until the following season, and only played with six players. In every game, the winner was the one playing under its league's rules. The Torontos won Games 1 - March 20, 1918 and game 3 - March26, 1918, with victories of 5–3 and 6–3, and the Millionaires recorded 6–4 and 8–1 wins in Games 2 - March 23, 1918, and 4 March 28, 1918. Because game five - March 30, 1918, was played under NHL rules, it helped Toronto's Corbett Denneny to score the series winning goal in a 2–1 victory. The Torontos outscored the Millionaires by a combined total of 13–7 in the three games played under NHL rules. Conversely, Vancouver recorded a 14–5 margin in the games under PCHA rules.