Adam Armstrong struck twice as Southampton booked a place in the Championship play-off final with a thumping 3-1 victory over West Brom on a raucous evening at St Mary’s.Midfielder Will Smallbone set Saints on course for a Wembley showdown with Leeds on May 26 by lashing home the opener four minutes into the second half.Top scorer Armstrong completed the job with a fine finish followed by a late penalty to take his tally to 23 goals for the season.twitter:1791571613684543673West Brom were second best on the south coast but claimed an added-time consolation through Cedric Kipre before jubilant Saints fans celebrated moving a step closer to an immediate top-flight return with a pitch invasion.Southampton finished 12 points above Albion and did the double over their opponents during the regular season but were unable to establish an advantage during Sunday’s cagey first leg at the Hawthorns.Saints boss Russell Martin, who remained without influential striker Che Adams due to injury, recalled Ryan Fraser and David Brooks following that goalless draw, while the visitors brought back captain Jed Wallace in place of Brandon Thomas-Asante.Home fans packed the road outside the ground long before kick-off to welcome the team bus, setting the tone for a boisterous affair inevitably tinged with tension.Brooks threatened a 16th-minute breakthrough when he brushed the outside of the right post following Armstrong’s cutback before Saints goalkeeper Alex McCarthy turned an overhit Tom Fellows cross on to the bar and over at the other end.For all of the anticipation among the crowd, which included Prime Minister Rishi Sunak – a lifelong Southampton supporter wearing a black Saints hoodie there was initially a distinct lack of goal-mouth action.Bournemouth loanee Brooks brought a routine save out of Baggies keeper Alex Palmer from distance as the stalemate of five days earlier persisted until the interval.West Brom seemed happy to stifle their hosts and await opportunities on the break.But the Baggies were architects of their own downfall only four minutes after the restart as the stadium exploded into life.Smallbone intercepted Grady Diangana’s sloppy pass just inside Saints’ half and, having advanced forward and received the ball back from Brooks, took a couple of touches before rifling home a rising drive via the right post.Albion were forced to release the shackles and should have levelled nine minutes later.The unmarked Alex Mowatt was picked out by Fellows’ pull back from the right but, with the goal gaping, his scuffed effort was unconventionally blocked behind by the head of Taylor Harwood-Bellis.Brooks continued to be a key figure in the contest and felt aggrieved not to be awarded a 57th-minute penalty when he was wiped out from behind by Baggies defender Kipre following a poor clearance from keeper Palmer.McCarthy acrobatically turned over a rising drive from Darnell Furlong before Saints sealed a date at the national stadium later this month.Armstrong, who earlier was denied by an offside flag, found space inside Albion’s 18-yard box to drill a low, angled finish through the legs of Furlong and into the bottom right corner 12 minutes from time.Slim hopes of an Albion fightback were extinguished in the 86th minute when Ryan Manning was felled by Fellows and Armstrong powered into the right corner from the spot.Kipre headed in from Mikey Johnston’s corner in the sixth minute of added time but the Baggies were powerless to prevent Saints marching on.