By James Cormack Manchester United cruised to all three points at St. Mary’s on Saturday afternoon with Alejandro Garnacho adding some gloss to the eventual 3-0 scoreline with the final kick of the game. There were structural issues once again in the first half as a change in tack from Russell Martin facilitated a notable Southampton improvement from their opening three performances of the season. United were second-best for much of the first half, but the contest was turned on its head when Andre Onana denied Cameron Archer from the penalty spot. Archer’s effort from 12 yards in the 33rd minu…