From the rubble to the Ritz? The stirring pre-match reception ­Southampton’s supporters gave their players left a wreckage of flares, smoke bombs, empties and cans but as fans exited a supercharged St Mary’s they departed with a trip to ­Wembley to plan.

Russell Martin’s side were given a heroes’ welcome and now they are one game from returning to the Premier League at the first time of asking, a date with Leeds to prepare for a week on Sunday. Will Smallbone settled any lingering nerves, opening the scoring early in the second half, before Adam Armstrong struck twice late on, firing in with a precise strike before sealing victory from the penalty spot.

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After taking the decision to arrive together on the team coach, Southampton’s players were greeted by a haze of red smoke, a fan-led guard of honour of sorts. The Ellisons bus driver who navigated the carnage made himself an early contender for man of the match, long before ­Taylor Harwood-Bellis, Flynn Downes, David Brooks and Armstrong took centre stage.

Martin said: “The noise was incredible, the passion of the people, the lads started seeing their family in the crowd, I saw my brother and son – it was amazing. I’ve never seen anything like it – there were a lot of emotional people on the bus on the way in and it made my team talk really easy.”

There was a discernible beauty to this Southampton performance: all neat patterns, fluid energy, every part interminably interchangeable, slick, sharp attacks. Amid a backdrop of dark arts. Southampton purposefully added a ring of advertising hoardings – in the name of the Saints Foundation – to squeeze space on the touchline for the West Brom defender Darnell Furlong to have a run-up for long throws.

It was uncharitable but not, as Carlos Corberán gracefully accepted, foul play. “When you do things inside the regulations, it is fair,” West Brom’s head coach said, before bemoaning his side’s delayed arrival into the away dressing room owing to the pre-match fanfare. “We were waiting 15 minutes on the bus. Unfortunately, the strongest team on the pitch achieved our target.”

It all felt a bit tit-for-tat; Southampton were unhappy with what they felt was a dry pitch at the Hawthorns in the first leg and West Brom with the lack of communication on arrival here, but they were trivial complaints compared to the unsavoury scenes at the final whistle. A section of Southampton supporters piled on to the pitch and goaded the travelling fans, with missiles, seats and flares thrown back and forth before police and stewards got things under control.

“I haven’t seen it but I think it’s unnecessary and I’m pretty sure it will be a real, real minority,” said Martin of the incident. “Our fans were amazing tonight. For those who did do that, if it tarnishes the night we’ve had and the win we’ve had and getting to Wembley in any way then they’ve let themselves down. But hopefully it was really very few people and hopefully the majority had a brilliant night, and they were great.”

Martin says the best day of his footballing life was captaining Norwich to the Premier League via the Championship playoff final in 2015 and Southampton made no attempt to play down the significance of this occasion. The hosts made sure to embrace it, evidenced from the carnival atmosphere outside the Itchen Stand two hours before kick-off. “The players showed so much courage,” Martin said. “The challenge now is to do that on the biggest stage, be themselves and be the team we want to be. We have the chance to have the biggest and best moment next week and now we need to make sure that’s the case.”

The first leg was a slow-cooked contest and at half-time here the teams were still locked at 0-0 despite Southampton dominating. There was a tangible buzz among the home support – Rishi Sunak was among those in the directors’ box, along from the club’s majority owner, Dragan Solak, who was bobbing up and down after Armstrong’s spot-kick – and, in truth, Southampton never looked like losing, Cedric Kipré’s headed consolation a rare West Brom effort on goal.

Brooks was outstanding, clinking a post in the first half after meeting Armstrong’s cutback and teeing up Smallbone to strike in off the woodwork in the second. Smallbone started and finished the move, cutting out a loose pass from Grady Diangana and then driving forwards. Smallbone handed the baton to Brooks, who ushered a pass into to his path with the outside of his left foot. Smallbone took a couple of touches and then took aim, his right-foot shot kissing the woodwork en route past Alex Palmer in the visitors’ goal.

Southampton should have had a chance to double their lead from 12 yards approaching the hour but the referee, Tim Robinson, did not award a penalty despite Kipré wiping out Brooks in the box before taking the ball. Not that it would matter, Armstrong killing off West Brom with an arrowed strike on 78 minutes before adding the third from the spot to seal a place at Wembley.