Willingham's two-out double off Aaron Laffey (0-1) gave the Athletics a 3-1 lead and helped Oakland earn a split of the four-game series. Willingham added a run-scoring single in the ninth inning.
Anderson (2-1) gave up two runs - one earned - and five hits in seven innings. He struck out six and walked one.
Brian Fuentes entered with two on and two out in the eighth and struck out pinch hitter Luis Rodriguez. Fuentes struck out two more in the ninth while recording his sixth save of the season.
Oakland picked up a pair of runs in the ninth with Coco Crisp scoring when Chone Figgins made an error on Conor Jackson's grounder and Willingham singling home Daric Barton.
The Athletics took a 1-0 lead in the first on Hideki Matsui's run-scoring single. Seattle tied it in the bottom of the inning when Ichiro Suzuki scored on Milton Bradley's groundout.
After Willingham's double drove home Crisp and Jackson in the seventh, the Mariners tallied in the bottom of the inning when Michael Saunders scored on Ryan Langerhans' infield out.
Crisp went 3-for-5 and scored three times.
Seattle starter Doug Fister gave up one run and four hits in six innings.
