Southampton advanced to the playoff final against Hull City, though it seems unlikely it will be quite that straightforward from here owing to the alleged foul play that dominated the buildup to a fraught second leg that went the distance, more than 130 minutes in total. If found guilty of cheating, Middlesbrough will demand Southampton are adequately punished. Is there even a world where Kim Hellberg’s train for the next couple of weeks in the event of the unprecedented?

Just what is it about Shea Charles and big moments, his latest coming in the 116th minute to send Tonda Eckert’s side to Wembley? It was the midfielder who scored the winning goal to send Arsenal packing in the FA Cup quarter-finals, his 96th-minute winner that clinched the 4-3 comeback victory against Leicester in February and now this. Charles was out on the right flank, the game edging towards a penalty shootout, when he sent the ball in with his left foot – it was surely a cross – and the ball sailed past the Boro defender Dael Fry and in at the back post.

The game itself was a mountain of flashpoints, not to mention the pre-match controversy. Towards the end of the first half the referee, Andy Madley, had a word with both 30-something head coaches after Taylor Harwood-Bellis allegedly made discriminatory comments to Luke Ayling, goading the Boro defender about his stammer. And then deep in the second half, a Southampton ballboy enjoyed a contretemps with Aidan Morris after refusing to hand Matt Targett the ball.

There was an extraordinary backdrop to the tie, the Championship’s spygate 2.0 subplot undeniably taking centre stage since the English Football League charged Southampton with two counts of misconduct on the eve of Friday’s first leg. On the morning of the game, Southampton’s chief executive, Phil Parsons, confirmed the club had launched an internal review but have requested time to provide the independent disciplinary commission with their side of the story.

Some Southampton fans again leant into the accusations, which the club have not denied and are not expected to contest, by donning fancy dress making light of the fanfare. Wallet, keys, phone, pot plant? Not quite, but a couple of supporters opted for full camouflage ghillie suits, others just a pair of binoculars.

There was never likely to be any shortage of needle and from the moment Middlesbrough’s team coach was targeted with an array of missiles on arrival, a hot atmosphere ensured a busy night for the officials. In the moments before kick-off Eckert emerged from the tunnel to locate Hellberg on the edge of the away technical area and shake hands. With 38 minutes on the clock, the fourth official, Tom Nield, found himself caught in the middle as Eckert and Hellberg exchanged words, an incensed Eckert agitating towards his opposite number.

At that point Saints were growing into the game but behind to an early first-time strike by Riley McGree, who converted Callum Brittain’s cross from close to the penalty spot after a little more than four minutes. McGree’s finish spun into the bottom corner past Daniel Peretz and the Boro midfielder showed impressive restraint to resist the urge to do a spy-related celebration, instead mimicking an emu, something he has done since his days in the A-League with Adelaide United.

Boro racked up a total of 21 shots in the reverse leg, five on target compared to Southampton’s none, and registered more than five times as many touches in the opposition box. Here they seized their first chance and then Morgan Whittaker rattled the side netting on 10 minutes. From that point, however, the hosts dialled up the pressure. Ross Stewart, on the stretch, hooked wide after latching on to Ryan Manning’s superb cross and then Casper Jander pickpocketed Morris on the edge of his own 18-yard box but could not find a teammate in red-and-white stripes.

Southampton’s equalising goal came from a James Bree free-kick, first-half stoppage time looming. Bree picked out an unmarked Manning at the back post and the left-back’s volley thudded into the ground and was repelled by Sol Brynn in the Boro goal. The danger was not over there and Stewart climbed highest above a clutch of players to head in across goal. Cue the sound of Zombie Nation over the speakers and St Mary’s was a different proposition. “We spy when we want,” came the chant from the home fans, presumably a line not endorsed by the club.

There was little letup in a breathless match. The former Boro midfielder Finn Azaz was booked for a slide tackle on a former Saint in Matt Targett. The big calls kept coming for the referee, Madley, none more so than when Ayling played a dangerous game in the box, putting his right hand on Léo Scienza’s chest and destabilising the advancing Brazilian at the critical moment after Stewart outmuscled Fry and cleverly spread play. Eckert went berserk on the touchline, screaming injustice, arms wide open. Madley wagged his index finger, insisting there was no foul. A few minutes earlier Ayling was again involved when, at the end of some chaotic defending, the Boro defender diverted Manning’s low shot wide. Southampton were undoubtedly in the ascendancy, Boro forced into a change when Tommy Conway limped off.

Eckert introduced Flynn Downes in search of further control and then Cyle Larin and Sam Edozie. Larin forced Brynn at the start of at least six minutes of second-half stoppage time, by which point Boro appeared far leggier. McGree was penalised for a tired challenge on Azaz and then Fry collided with Larin. It was a theme that continued into extra time, Brittain booked for fouling Edozie. The game was full of unforced errors and Saints seized on Boro being on their last legs.