Notre Dame began the day leading the nation in field-goal shooting (52.2 percent) and 3-point shooting (44.9 percent), but the Irish shot 36 percent overall in the first half and 1 from 6 on 3s.
"Definitely credit their defense," McGraw said. "We got good looks, but we really missed the shots that normally we'll make."
With 1:25 left, however, Ariel Braker got a steal off an inbounds play for Oregon State, and McBride made a jumper to push the lead to 66-58. Braker blocked Weisner on the Beavers' next possession.
McGraw said defense was critical to the comeback.
"When we contained the ball and didn't give them driving lanes, we were able to really shut them down," she said. "They couldn't kick it out to wide open shooters."
Sophomore Jewell Loyd, last year's national freshman of the year, had 10 points for the Irish — 8.5 below her team-leading average coming in.
The Irish, who have reached the Final Four each of the last three years and title games in 2011 and 2012, are off to their best start since 2009-10, when they began 15-0.
Notre Dame's next game is Jan. 2 against South Dakota State.
Weisner, a sophomore guard, entered the contest as the Beavers top scorer at 14.9 points per game. OSU has a young team, with four underclassmen starters.
Sunday's game was the start of a tough stretch for the Beavers, who open Pac-12 play next week with games against No. 23 California and No. 4 Stanford.
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