Despite Barcelona being on Europe's longest unbeaten streak and looking formidable before the game, there were plenty of things that made the Eintracht defeat possible.
1. No-risk starting XI
Barca were hoping for Gerard Pique to make it to the game – but he wasn't even present on the bench.
Xavi decided against risking Sergino Dest's health, Clement Lenglet looked too error-prone last time out, hence why Oscar Mingueza started at right-back.
There were some midfield problems too: Frenkie de Jong had been ill for 2 days and was only available for 45 minutes.
As a result of this, Xavi had little to choose from, relying on the best available starting roster.
2. Poor physical state
Eintracht Frankfurt once again looked much better in this respect.
It was too difficult for Barca players to win ground duels and compete for the ball the way they usually do under Xavi. The Blaugrana boss himself has agreed there was no needed intensity from his players.
Unlike the German side that seemed to have been saving energy for the second leg on Sunday (they lost to Freiburg 1-2 and had a bang-average second-half performance), Barca had a late kickoff against Levante the same day and had to rescue themselves on a very wet pitch until the very last minute of the game.
We can't be surprised.
3. Injury calls during the game
Ronald Araujo was seen with a bandage late in the first half. This was also the moment Pedri picked up an injury that possibly means his season is over.
At half time, sick Frenkie de Jong was forced to play the game remainder.
4. Awful attacking display
Ousmane Dembele looked like the 'good old' Ousmane whose only standout attributes were speed and dribbling. Ferran Torres didn't impress either. Pierre-Emerick Aubameyang unbelievably missed a sitter (back to those Arsenal-in-Europe days?) at a very important moment of the game.
Despite not being as clinical as usual, Luuk de Jong actually improved Barca upfront – this says a lot about the three defenders that started the game on Thursday.
5. Poor refereeing
Before Filip Kostic put the ball into the net in the 4th minute, Eintracht's Daichi Kamada ran into the box and the penalty kick should've been re-taken.
There was no penalty call in the second half for some reason, although the Eintracht player definitely made a move with his hand that changed the ball direction. Besides, the arm was not close to the body.
Finally, the referee didn't let Barca come up with the final attack after they scored the second goal. There were enough pauses in the stoppage time - partly for Eintracht's time-wasting - for the referee to add a minute or two to what he added initially.
6. Bad luck
Despite a worrying first-half performance, there were moments when Barca were really pilling on the pressure after the break.
Ronald Araujo moved to a striker position and was really unlucky not to score – same with Luuk de Jong who almost put it in before Barca finally scored their first. Sergio Busquets was inches offside when Barca's goal got disallowed.
7. Fan controversy
The biggest off-the-pitch highlight was the number of Eintracht Frankfurt fans in the stadium.
No more than 5,000 away fans were expected to be at Camp Nou – but the club seemingly preferred to make more tickets available for Eintracht supporters - who are generally richer than the Barcelona citizens.
Also, there are rumours that some of the season ticket holders were selling their tickets for pennies ahead of the game – Eintracht fans were among the buyers too.
Around 20,000 Eintracht supporters were on the stadium on Thursday. This should not be an excuse for Xavi and his team, but this certainly didn't help them at all.
