Southampton beat Middlesbrough 2-1 at St Mary's to book their place in the Sky Bet Championship play-off final for the second time in three seasons.
After a goalless first leg on Saturday, Riley McGree slotted Boro into an early lead on the south coast, but Ross Stewart levelled with a towering header on the stroke of half-time.
The score remained locked at 1-1 after 90 minutes and penalties were looming when, with 116 minutes on the clock, Shea Charles' cross from the right evaded everyone and bounced past Sol Brynn into the back of the net.
Tonda Eckert's men will play Hull at Wembley on Saturday May 23, with a lucrative place in the Premier League on the line.
The tie was overshadowed by 'Spygate' with Southampton charged with a breach of EFL regulations after a member of staff was alleged to have spied on Middlesbrough's training ahead of the first leg.
Southampton have asked the EFL for more time to conduct an internal review as they cooperate with a disciplinary commission.
Middlesbrough were overwhelmingly dominant in the first half of the first leg, with 17 shots and a combined xG value of 1.39, but they could not make the breakthrough. Within the first five minutes of the start of the second leg, they did.
Callum Brittain fed a low cross into the box, and the home defence just seemed to freeze for a split-second as McGree swept the opener into the bottom left corner.
For a few minutes, Saints looked shell-shocked. But when they regained their composure, they came within inches of the equaliser when Ryan Manning's exquisite cross was steered past the left-hand post by Stewart on the stretch.
Stewart atoned for his miss in first-half stoppage time. Sol Brynn saved Manning's initial effort, but the ball spun to the other side of the box, where the striker leapt like a salmon to power in a header.
Just before that, tensions had threatened to boil over. Referee Andy Madley beckoned Tonda Eckert and Kim Hellberg over on the touchline and, after a brief exchange, the pair had to be separated.
Asked in his post-match press conference about the incident, Hellberg said: "It's the heat of the moment and feelings and emotions. We love that about football. That's one thing we really, really love. When it happens on the pitch it is what it is, feelings and emotions in a big game. Nothing big."
As it transpired, Southampton's Taylor Harwood-Bellis was alleged to have made a discriminatory comment to Middlesbrough's Luke Ayling, which Ayling reported to the referee. He then discussed it with the head coaches.
Your Site News understands Madley will report the incident to the EFL.
Harwood-Bellis and Ayling did appear to converse amicably and hug towards the end of the game.
Of that situation, Hellberg said: "That's not my place to say. On the pitch, things happen. It's not my role to explain. It's better the people involved do that."
Both teams had penalty shouts turned down before the midway point of a second half where chances came at a premium.
Middlesbrough were furious not to be awarded a spot-kick after Kuryu Matsuki appeared to handle the ball in the box, before Saints were denied one when Leo Scienza was pushed off the ball by Ayling.
There was another in second-half stoppage time. Dael Fry went to swing to clear a ball, but Cyle Larin nipped in, took the ball away and went over after clashing with the Boro defender. Madley immediately waved away appeals.
Your Site' Simeon Gholam:
"It feels like it was a spot of controversy that got lost in the mix with so much else happening, but both sides had genuine penalty shouts waved away by Andy Madley in the second half. Three in total - a handball, a push and a late tackle.
"This was Madley's first second-tier game since February, and just his third all season.
"On Saturday, Madley dished out yellow cards twice in the Premier League game between Bournemouth and Fulham, on both occasions being sent to the pitchside monitor to then upgrade them to red cards.
"It seemed a reluctance to make a match-altering decision without the safety net of a video review. Should VAR be in use for the semis to align with experiences referees now have regularly in the Premier League?"
Middlesbrough were running out of steam towards the end, but looked to be limping towards a penalty shootout. It seemed the best-case scenario at that point.
Saints kept going, though, and finally got their reward with four minutes of extra time to play, when Charles' cross found its way past Brynn.
Boro did push to try and level up in the dying embers, but their efforts were in vain.
It did not end at full-time at St Mary's, as the drama continued into the post-match press conferences.
Hellberg was clearly devastated, suggesting 'Spygate' had stolen away his Premier League dream.
"I worked 15 years as a coach, trying to get to the Premier League. That's my dream for 15 years," he said, later adding: "It breaks my heart in terms of all those things I believe in. That's the thing. I don't care if there are other rules in different countries.
"This is England where football is the biggest thing. That's my feelings about it. I think it's disgraceful. It makes me very sad."
Asked if he believed Tonda Eckert knew of the alleged 'spying', Hellberg said, simply: "I cannot answer. No comment."
Eckert, meanwhile, abruptly left his press conference again, after being asked if he was a cheat. This drama will rumble on.
