Mussina held the Royals scoreless for an entire eight innings, scattering four hits and four walks while striking out five batters. He earned just his second victory in his last seven starts and lowered his ERA to 3.19.
Mariano Rivera worked into and out of trouble in the ninth inning, but struck out Dee Brown looking to end the game.
The Yanks put up one run in six different innings to down Kansas City, who was held to six hits after pounding out 14 in the first game of the series.
Posada drove home Bernie Williams with a double to start the scoring in the first inning. He added his 20th homerun of the season in the sixth inning to give New York a 4-0 lead.
Derek Jeter hit an RBI single in the third inning to plate a run, and Todd Zeile made good use of a rare start by driving in a run with a sacrifice fly in the fourth. Nick Johnson and Williams added RBI singles in the eighth and ninth innings to cap the scoring.
Darrell May (5-6) took the loss for the Royals. He allowed five runs on 12 hits and a walk over 7 1/3 innings while striking out just one. Al Levine allowed three hits and a run in relief to give the Yankees 15 hits for the second straight night.
The rubber match of the series will be on Wednesday at 8:05 pm eastern time. Jeff Weaver (6-8, 5.44) will take the mound looking to win the series for the Yankees. Kevin Appier (7-8, 5.53) will make his second start as a member of the Royals this year.
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