What do you mean by "breakthrough season" and if a player plays half his club's games in the season after his breakthrough season, why shouldn't he count as an academy graduate who has become a first team regular?
Saints beat Derby 4-2 in the semi-final
Ryan Seager hat-trick
Final against Blackburn.
http://www.saintsfc.co.uk/news/article/20150305-u21-report-southampton-4-2-derby-county-2317324.aspx