Mariano Rivera pitched an inning of a simulated game Thursday morning and came away more pleased by the balls he caught than by the ones he threw. "What do you guys think, huh?,'' Rivera asked a group of reporters who watched his 18-pitch session on the back field at George Steinbrenner Field. "How was the fielding?'' Rivera had already thrown to hitters last week, but had yet to field a ball off the mound, one of the last hurdles in his recovery from surgery to repair a torn ACL in his right knee last May. This time, however, he needed to come off the mound quickly three times -- once to cover first on a bunt, another time to field a bunt up the first-base line, and the third time to cut off a bouncing ball between first base and the mound.