The Red Sox already added a spark to their lineup by promoting one of the top prospects in baseball in August. Andrew Benintendi took over in left field and hit .324/.365/.485 in 21 games before spraining his left knee a week ago. With big league rosters expanding to 40 for September, Boston is hoping to get similar impact by calling up the game’s best prospect. Infielder Yoan Moncada, ranked No. 1 on MLBPipeline.com’s Top 100 Prospects list, will join the Red Sox Friday in Oakland.