Mesén eventually became an understudy to Rojas who was the first-choice goalkeeper, and rose to first-choice keeper himself ahead of the 1997-98 season, when Rojas's career ended at Alajuelense as a result of being on the receiving end of an eight-match ban (as he was involved in a post-match brawl after a match against Saprissa in June 1997--Mesén also was involved in said brawl but received a minor ban), causing the Alajuelense's Board of Directors to show him the door as Rojas was going to be unavailable for six matches (having served two on the 1996-97 season's finals).