Red Sox right-hander Aaron Cook will make his first big league appearance of the year on Saturday as a starter, in place of Josh Beckett, who has lat tightness. Cook, 33, was 3-0 with a 1.89 ERA at Triple-A Pawtucket. He last pitched on Saturday, which will put him on six days of rest. He signed a split Minor League deal with the Sox during the offseason that included two opt-out dates, May 1 and June 1.