Dan Pasqua drove in four runs with three hits, including a three-run home run and a double, and Don Mattingly hit a two-run homer for New York at Seattle.
The Yankees, who have won 10 of their last 11 games, and 17 of 19, moved within three games of Toronto in the East Division.
Pasqua, who had gotten two hits in 15 at bats since being recalled from the minors Aug. 16, hit his three-run homer in the first inning off Mike Moore (11-8). He also singled in the fourth and doubled in a run in New York's two-run sixth.
Mattingly's 23rd home run brought his season RBI total to 104.
Ed Whitson (8-7) stopped Seattle on one hit for six innings, then was routed by two-run homers by Alvin Davis and Jim Presley, his 25th.
"He was in a slump when he came back," New York Manager Billy Martin said of Pasqua. "He was even in a slump in batting practice."
"Lou Piniella (batting coach) has been giving me little tips each day. Each little thing he tells me helps," Pasqua said. "I just have to keep working hard and hope it becomes habit."