The third-seeded Eagles (20-10) held the sixth-seeded Black Knights (12-18) to 11 first-half points on their way to setting up a semifinal at Lehigh Saturday.
The second-seeded Mountain Hawks split the regular-season series with American, with each team winning at home.
Ella Ellis recorded his second double-double of the season with 13 points and 10 rebounds as Army’s season came to a close.
The Eagles held the Black Knights to just 26.3-percent shooting (15 of 57), their worst offensive effort of the year.
Army shot 16.7 percent (4 of 24) during a first half when American built a 23-11 lead, while forcing Army into 10 first-half turnovers.
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