Maya Moore added 16 points and Rebekkah Brunson had 12 points and 11 rebounds for the Lynx. Whalen also had six assists and four rebounds.
Rookie reserve Shekinna Stricklen had 13 points to lead Seattle. Katie Smith and Lauren Jackson added 12 points each.
Seattle twice rallied to pull within six points in the final 12 minutes, but Minnesota 16-1 at home in the regular season, pulled away again each time.
Game 2 is Sunday at Seattle.
The Lynx started the second half on a 15-8 run to extend their six-point halftime lead to 17 on Candice Wiggins' 3-pointer with 2:38 left in the third quarter. However, the Storm finished the period on an 11-3 run to keep it close. Augustus scored eight points in the period for the Lynx.
Minnesota extended its lead to 12 points on Brunson's jumper with 5:06 to play. Seattle responded again with an 8-0 run, but Moore and Augustus made clutch shots in the final two minutes and the Lynx made 5 of 6 free throws in the last 32 seconds to seal the win.
Minnesota, which took three of four from the Storm during the regular season, turned the ball over nine times in the first 20 minutes and led just 33-27 despite Seattle's 29-percent shooting from the floor.
The Storm shot just 39.7 percent from the floor and never led. Minnesota improved to 18-0 when holding opponents below 40 percent this season.
The Lynx and Storm are matching up in the postseason for the first time since the 2004 Western Conference semifinals, which Seattle swept en route to the first of its two league titles.
Minnesota is trying to become the first back-to-back champion since Los Angeles accomplished the feat in the 2001 and '02 seasons. The Houston Comets won the league's first four titles from 1997-2000.