Yankees starting pitcher C.C. Sabathia (12-3) allowed one run over seven innings to pick up the win, his eighth consecutive victory. He is one of eight Yankees selected to go to the All-Star Game.
"He just finished off what he started on Tuesday. Outstanding starting pitching," Yankees manager Joe Girardi told reporters.
New York's Mark Teixeira had four hits with one RBI and two runs scored. Marcus Thames drove in two runs, as did Derek Jeter.
The Mariners did themselves no favors with a pair of errors in the first inning that led to two runs, and a wild pitch in the third allowing the Yankees to extend their lead to 3-0.
Two more wild pitches in the fourth inning marked the end for Mariners starter Ryan Rowland-Smith (1-9), who allowed six runs on six hits with a walk and a strikeout.
"It's tough," Rowland-Smith said. "Like I said, with that lineup you can't give them that many chances. They're going to capitalize on them and that's what they did."
Robinson Cano led off the fifth inning with a double off Mariners' reliever Brian Sweeney and two batters later Thames launched a two-run home run to complete the Yankees' scoring.
The Mariners scored a run in the sixth inning on three consecutive singles off Sabathia, and added another in the bottom of the ninth with a solo home run by Casey Kotchman off reliever Dustin Moseley.
(Reporting by Mike Mouat in Windsor, Ontario; Editing by Peter Rutherford)
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