The Blaugrana endured a miserable night on Merseyside as their chances of winning the Champions League this year were ended by a rampant Liverpool (U.S. only):
Leading 3-0 from the first leg, all Barca had to do was get one away goal to leave Liverpool needing five to advance to the final in Madrid on June 1.
Despite Messi's best efforts, Barca dramatically capitulated in the knockout stages of Europe's elite competition for the second year running:
To make matters worse, the Argentinian superstar then had to undergo a drug test after the final whistle, and by the time it was done the Barca bus had left for the airport without him, per El Chiringuito (h/t Metro).
Messi eventually rejoined his team-mates before they returned to Catalonia.
Barca have already wrapped up the Liga title, but they still have Getafe and Eibar to play before May 25's Copa del Rey final against Valencia.
A second consecutive domestic double looks well within reach for Barcelona, but this season will still go down as a disappointment given Tuesday's dire performance.
Barca were arguably fortunate to be going into the second leg with a 3-0 lead given the balance of play at the Camp Nou, but they effectively had one foot in the final following Messi's late double.
Everything looked to be set up for Barca to go on and win the Champions League. They had a rested side after manager Ernesto Valverde made multiple changes for Saturday's loss to Celta Vigo, and Liverpool were missing two of their key attacking players:
However, things started to go wrong early on for the visitors at Anfield when Divock Origi scored in the seventh minute.
A quick-fire double from substitute Georginio Wijnaldum early in the second half drew Liverpool level at 3-3 on aggregate, but even then Barca needed just one goal to get back on top.
Liverpool's fourth was the game in microcosm. Barca's defenders inexplicably switched off at a corner, Trent Alexander-Arnold took it quickly, and Origi swept home:
Barca must now resign themselves to another season of European disappointment, and it was a huge opportunity missed given the Catalans would have been favourites in the final against either Ajax or Tottenham Hotspur.