Leading by a point with less than 16 minutes to play, the Lumberjacks (8-9, 5-1 Big Sky Conference) scored 14 straight points and went on a 24-2 run to extend its lead to 62-39.
Northern Arizona shot 58.9 percent from the field, including 70.4 percent in the second half. Jacobsen hit 8 of 11 field goals while Yanku made 6 of 11. Quinton Upshur added 12 points and Gaellan Bewernick had 10 for the Lumberjacks.
Portland State (7-8, 2-4) went 5 of 21 from beyond the arc and got out-rebounded 36-21 by Northern Arizona. Gary Winston led the Vikings with 13 points.