Quadruple-chasing Chelsea fell to a heavy defeat in the first leg of their Women's Champions League semi-final with Barcelona.
Ewa Pajor gave Barcelona a first-half lead when she coolly slotted the ball past goalkeeper Hannah Hampton after being played in behind by Alexia Putellas' clever pass.
Substitute Claudia Pina doubled their advantage, poking home from close range midway through the second half.
However, Chelsea had proven to be a threat in spells and responded when wing-back Sandy Baltimore drilled an effort into the far corner to halve the deficit.
That looked set to give Sonia Bompastor's side a real opportunity in the second leg at Stamford Bridge next Sunday (14:00 BST) but Irene Paredes added a third goal for Barcelona late on.
As if Chelsea's evening could not get any worse, Pina rounded off an impressive evening for Barcelona with a fourth in stoppage time.
It is a third straight meeting between the sides at this stage of the competition, with Barcelona coming out on top in the previous two - and they will have enjoyed causing further pain in Spain.
England forward Aggie Beever-Jones came close for the visitors when her curling free-kick was pushed behind by goalkeeper Cata Coll, scrambling low to her left.
That came during a positive spell for Chelsea, who ended the first half on top despite trailing.
They had goalkeeper Hampton to thank for saving a first-half penalty from two-time Ballon d'Or winner Putellas.
Barcelona remain the team to beat in Europe and it was a tough evening for Chelsea, who have a lot of work to do in London.
"It was difficult just to lose the game but also to concede four goals," said manager Bompastor afterwards.
"These games are really difficult because Barcelona are one of, if not the best team in Europe.
"When the result was 2-1, we were not in a really bad situation because there was only one goal in it. But the last 10 minutes were not good enough."