Mariano Rivera whistled as he walked alone, head down, along the green carpet that led toward the clubhouse inside George M. Steinbrenner Field. He had just completed his second bullpen session of the spring, and as he explained later, “everything was good. Everything was right on schedule. Perfect.” His right arm “feels great.” His surgically-repaired right knee did not bark during the 25-pitch session. His pace was deliberate. Rivera took his time between throws, chatting in Spanish even as he toed the rubber. He wore a thin brace over his knee. “It doesn’t bother me at all,” he said. “It’s nothing. It’s like a sock. Only a little bit tighter.” As he eases into the rituals of spring, Rivera explained why he does not view his schedule as a series of hurdles. The act of pitching does not worry him. His only concern is trusting his knee during live competition. “If I’ll be looking for something, I’ll be looking for the games,” Rivera said. “The reason why is you have to react there: On comebackers, cover first, all that stuff. You can’t think. You have to react. That will be, I would say, the biggest test.”