For the 1905–06 season, the Ottawa HC (aka Silver Seven) joined the new Eastern Canada Amateur Hockey Association (ECAHA). In February, Ottawa played a best-of-three challenge series against OHA champion Queen's University, but the Senators proved to be the better team as they swept the series with 16–7 and 12–7 victories.

Date Winning Team Score Losing Team Location
February 27, 1906Ottawa HC 16–7Queen's UniversityDey's Arena
February 28, 1906Ottawa HC 12–7Queen's University
Ottawa HC wins best-of-three series 2 games to 0

About a week later, Smiths Falls, the FAHL champions, issued a challenge for the Cup, but they suffered the same fate as Queen's University. The Ottawas defeated them with scores of 6–5 and 8–2 to defend the Cup. Interestingly, Ottawa management was so impressed with Smiths Falls goalie Percy LeSueur that they signed him to join the Ottawas a few days after the series ended.

Date Winning Team Score Losing Team Location
March 6, 1906Ottawa HC 6–5Smiths FallsDey's Arena
March 8, 1906Ottawa HC 8–2Smiths Falls
Ottawa HC wins best-of-three series 2 games to 0

The 1906 ECAHA season ended a few days later after the Smiths Falls - Ottawa series, with both Ottawa and the Montreal Wanderers tied for first place with identical 9–1 records. It was decided to hold a two-game total goals series to determine the league champion, and thus who would keep the Cup. The first game was played in Montreal where the Wanderers promptly crushed the Ottawas, 9–1. Needing at least an eight-goal victory in the rematch in Ottawa, the newly signed LeSueur was named Ottawa's starting goalie, and the Ottawas jumped to a 9–1 lead to tie the series. But with under 5 minutes to go, Montreal's Lester Patrick scored twice to clinch the series for the Wanderers, winning the total-goals series, 12–10 and taking over the Stanley Cup.

Date Winning Team Score Losing Team Location
March 14, 1906Montreal Wanderers9–1Ottawa HC Montreal Arena
March 17, 1906Ottawa HC 9–3Montreal WanderersDey's Arena
Montreal wins total goals series 12 goals to 10
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