Southampton dispatched an ordinary West Brom side by scoring three second-half goals.
Will Smallbone opened the scoring with a fantastic finish following a Grady Diangana error.
Adam Armstrong applied a brilliant finish to put the Saints in total control of the tie.
Southampton's lively striker converted a late penalty to reflect a convincing win over their play-off rivals.
Cedric Kipre did grab a late goal but it meant little as the final whistle soon went.
Southampton made two changes: Ryan Fraser and David Brooks replaced Ryan Manning and Sekou Mara.
Che Adams was absent once again through injury and after links to Wolverhampton Wanderers, could have played his last game for the Saints.
West Brom made a change of their own as their talisman Jed Wallace came back into the fold in place of Brandon Thomas-Asante.
-
Story of the match
Southampton started the game on the front foot by not allowing West Brom any time on the ball.
After a drab away performance from Russell Martin's side, there was a lot more intensity about the home side in the early stages.
West Brom have been a well-renowned organised side this season and would seemingly be a tough defence to break down.
The away side were always looking for a threat on the counterattack and from a set piece, which nearly worked as Grady Diangana headed wide from a corner.
Tim Robinson had to make the first big call of the night as Brooks threw himself to the ground in the penalty area.
Brooks came close to opening the scoring as the Welsh international smashed the woodwork from the near post after intelligent forward play from Adam Armstrong.
Alex McCarthy was kept busy at the other end of the pitch as the experienced number had to tip over an awkward Tom Fellow's cross.
West Brom struggled in possession within the first part of the game as they were hounded by Southampton's press.
Brooks was the Saints’ main threat and produced the first shot on target when shooting from a distance straight at Alex Palmer.
The rest of the first half represented a cagey game of chess between two sides with so much to lose.
Southampton came out with the same drive they had in the first half and finally got their reward.
Will Smallbone picked up possession from Diangana's poor pass and then played a one-two with Brooks before beating Palmer from 20-yards.
It was a beautiful finish from Southampton's controller in the middle of the park.
Robinson had another penalty decision as the dangerous man Brooks was taken down from Cedric Kipre but nothing was given despite it looking like an obvious foul from the centre-back.
The onus was on West Brom to come forward after spending so much of the game defending.
The away side nearly got their equaliser as McCarthy had to tip over a Darnell Furlong thunderbolt.
Southampton were still pressing for more goals and did find the back of the net through Adam Armstrong only for the offside flag to deny him.
The former Blackburn Rovers centre forward was not waiting too long before he got on the score sheet.
Flynn Downes drove forward and played into Armstrong's feet before placing a finish into the corner and confirming Southampton's place at Wembley.
Carlos Corberan's side were simply outclassed on the night and never looked like getting back into the tie.
The home side wrapped the game up in style as they were rewarded a penalty late on after Ryan Manning was taken down.
Armstrong made sure of the Saints’ commanding position as their number nine slotted his effort away for his second on the night.
Kipre scored with a header in the dying seconds but would not console West Brom fans who knew they will be spending a thrid consecutive season in the Championship.
-
Man of the match- David Brooks
Despite Armstrong getting two goals on the night, Brooks was the one player making things happen for Southampton early on.
The on-loan Bournemouth winger was a constant menace throughout the game.
When the Saints were in the ascendency, it was Brooks who came up with the important assist for Smallbone’s goal, providing the necessary quality when it was needed.
If Southampton are going to beat Leeds at Wembley, Brooks will be a crucial player in their attack.
