They most recently exited a major league diamond on terms far different than their own. For Mariano Rivera, it was a long ride on a green cart that took him from the warning track of Kansas City's Kauffman Stadium into the visitor's clubhouse last May, the ligament charged with holding his right knee together shredded. For Derek Jeter, it was a long hobble from his shortstop position at Yankee Stadium to the dugout, carried on the shoulders of his manager, Joe Girardi, and a trainer moments after his left ankle shattered while he was trying to make a play in Game 1 of the American League Championship Series in October. It was no small matter, then, for the Yankees to welcome both of their cornerstones back to major league competition Saturday afternoon at Steinbrenner Field.