Marcelo Mayer, Boston’s No. 2 overall prospect, was promoted to the Red Sox and needed to get a ride to Fenway Park to start against the Baltimore Orioles on Saturday. The reason he didn’t drive himself: He lost his car keys “like three weeks ago.” Mayer was promoted from Triple-A Worcester when third baseman Alex Bregman was placed on the 10-day injured list with a significant right quad strain.