BALTIMORE — Rob Manfred was elected baseball's 10th commissioner Thursday, winning a three-man race to succeed Bud Selig and given a mandate by the tradition-bound sport to recapture young fans and speed play in an era that has seen competition increase and attention spans shrink. The 55-year-old Manfred, who has worked for Major League Baseball in roles with ever-increasing authority since 1998, will take over from the 80-year-old Selig on Jan. 25. It's a generational change much like the NBA undertook when Adam Silver, then 51, replaced 71-year-old David Stern as commissioner in February.