One half of this arena was a picture of dejection, the other pure disbelief: for the first time since 1947, Brentford will play in the top flight of English football. There were tears of joy in the stands and on the pitch, Mathias Jensen among those overcome with emotion. Ivan Toney and Bryan Mbeumo rushed inside to fetch their phones to share the moment and by the time Henrik Dalsgaard led his teammates to collect their winners’ medals, the Swansea end had long since emptied. Half an hour after the final whistle, Emiliano Marcondes and Jensen pretended to hoist a giant 12ft replica of the Championship play-off final trophy before a sun-drenched sea of red and white. Shortly after Dalsgaard and the Brentford captain, Pontus Jansson, ambushed Thomas Frank midway through an interview before giving their head coach the customary celebratory bumps. “Right now, I just want to get so drunk and then tomorrow we can think of the Premier League,” said Frank when the interview resumed moments later. Matthew Benham, the Brentford owner and lifelong fan, high-fived players on the pitch. As the pyrotechnics fizzed into the sky behind the winners’ podium, players made sure to drench Peter Gilham, aka Mr Brentford, the club’s matchday announcer since 1969. After suffering a flurry of heartbreaking failures on the big stage – they finally conquered the play-offs at the 10th time of asking – this time Brentford made promotion look like a doddle. They soared into an early two-goal lead courtesy of a nerveless Toney penalty and a cool Marcondes strike, and Swansea, overawed by the occasion, offered no reply. When Jay Fulton was sent off midway through the second half, Brentford supporters decided to kick-start the party. No voodoos or hoodoos could stop them now. Swansea never settled, with the captain Matt Grimes’s crude challenge on Sergi Canós an early indicator of the angst that ate away at Steve Cooper’s side. Four minutes later, Freddie Woodman panicked as the electric Mbeumo, one of six players to start both this game and last season’s extra-time defeat to Fulham here, stormed through on goal and proceeded to bring down the forward, who had eluded Ben Cabango. Canós sliced open the Swansea defence with a teasing reverse pass and up stepped a typically unflustered Toney to dispatch the spot-kick, his 33rd goal of the season. Swansea were rattled. Woodman ballooned a pass out of play and Cooper was cussing as Brentford poured forward on the counterattack 10 minutes after the opener. As soon as Mbeumo collected a Brentford clearance a few yards inside his own half, Cooper turned to the away dugout, the pain etched on his face, presumably having foreseen the result of the two-v-two scenario that was about to play out. Brentford zoomed forward and Mbeumo forced the Swansea defender Kyle Naughton to back up before waiting for the overlapping Mads Roerslev, who popped up on his left. Roerslev picked out the arrival of Marcondes, who rounded off a slick break at the back post. Brian Riemer, the Brentford assistant coach, almost lost his step amid the celebrations, jumping the advertising hoardings to leap on to Frank. Brentford had made this pitch their playground and Toney came within centimetres of adding a spectacular third a minute later. He controlled a bouncing ball on his chest before letting rip with a right-foot strike that beat Woodman but walloped the crossbar. Toney gnawed at Swansea’s youthful centre-back partnership and Mbeumo proved a constant menace. Naughton was fortunate to avoid a foul after losing a battle on halfway and Mbeumo surged towards goal after seizing an aimless Marc Guehi header but failed to generate any power on his shot after swivelling clear of his marker. Brentford felt they should have had another penalty before the interval, when Vitaly Janelt’s powerful shot smacked the left hand of Jake Bidwell but the referee, Chris Kavanagh, penalised Toney for a foul in the buildup. Toney would have surely added a third but for a smart block by Bidwell late on. Swansea’s supporters belted out the Welsh national anthem with gusto before kick-off but their team fell painfully flat. They roused before half-time, with André Ayew nodding a header on to the roof of the net and two minutes after the break Ayew again went close, heading wide from Connor Roberts’s brilliant cross, which was mistakenly waved through by Jansson. With 25 minutes to play it was game over. Fulton appeared to slip and inadvertently lunged into Jensen. The referee immediately reached for his back pocket. Fulton pulled his shirt over his face as he trudged down the tunnel and up in the stands a Swansea supporter put both hands on his head. At the other end Brentford revelled in the catastrophe.