The A's won the first half of the split season format instituted for the 1981 season. Underwood faced just one batter in the 1981 American League Division Series with the Royals, striking out Willie Aikens. The A's swept the Royals in the ALDS to face Underwood's former team, the Yankees, in the 1981 American League Championship Series. The Yankees swept the series, with Underwood pitching in games one and three.