Willie Randolph hit his first home run of the season and Billy Sample and Bobby Meacham each had four hits as New York won at Oakland.
Ex-Oakland star Rickey Henderson had three hits, scored two runs and got his 13th stolen base in 13 attempts with the Yankees.
Ron Guidry (5-3) gave up four hits over eight innings for his fourth straight victory. The only runner he allowed past first base was Dwayne Murphy, who hit his fifth homer in the eighth inning. Bob Shirley pitched a hitless ninth.
The Yankees, who got 19 hits, scored an unearned run in the first when Dave Winfield brought Henderson home with a sacrifice fly. They pulled away by scoring at least two runs in the fourth, fifth, sixth and seventh innings.
Randolph lined his homer over the left field fence in the fifth, making the score 6-0, after Henderson led off with a double. The Yankees knocked A's starter Bill Krueger (4-4) out of the game in the sixth when they added two runs on Meacham's RBI double and Ken Griffey's sacrifice fly.
New York first baseman Don Mattingly sat out because of a slightly pulled groin muscle. Rookie infielder Rex Hudler started in his place, borrowing a glove and playing his first big league game at the position. Yankees reserve outfielder Henry Cotto punctured an eardrum with a cotton-tipped swab early in the game and was taken to a hospital.