Southampton defeated West Brom 3-1 on Friday night, to qualify for the Championship play-off final.
The first leg ended 0-0 at the Hawthorns last week.
The Saints are looking to make an immediate return to the Premier League and opened the scoring four minutes after the break through Will Smallbone.
Southampton then made sure with an eight-minute brace from Adam Armstrong.
There was, however, enough time for Cedric Kipre to head in a late consolation.
Southampton will now face Leeds in the final, as both teams look to clinch the last promotion spot after Leicester City and Ipswich Town.