Matt Cain will start. And for that, Buster Posey is relieved. Posey expected to be using his catcher's mitt as a butterfly net at the All-Star Game on Tuesday night, where he faced the prospect of snaring floating pitches from New York Mets right-hander R.A. Dickey. "I've never caught a knuckleball guy before,'' the Giants catcher said Monday. Instead, Posey gets the familiar repertoire of his teammate. N.L. Manager Tony La Russa chose Cain as his starter, in part because of the familiarity between the Giants battery. And by the time Dickey comes into the game out of the bullpen, Carlos Ruiz is expected to be behind the plate.