Concise News reports that Atletico thus missed the chance to mathematically guarantee they finish second in La Liga ahead of neighbours Real Madrid.
Espanyol took the lead right before halftime when Atletico captain Diego Godin slid the ball into his own net as he scrambled to clear a cross from 20-year-old left back Adria Pedrosa, who had burst forward from his own area on the break.
The Catalans’ top scorer Borja Iglesias doubled the home side’s lead early in the second half as they again pounced on the counterattack after an Atletico giveaway, with the striker calmly tucking the ball past Jan Oblak from inside the box.
Espanyol missed several chances to score again but Iglesias deepened Atletico’s humiliation by converting from the penalty spot in the 89th minute and also completing his side’s biggest league win of the campaign.
Atletico, who have now lost six times this season, are second in the standings on 74 points after 36 matches, nine behind champions, Barcelona, who play at Celta Vigo later on Saturday, and nine ahead of Real, who host Villarreal on Sunday.
Espanyol climbed up to eighth with 47 points.
Atletico midfielder Koke fiercely criticised his side for their limp display, particularly in the second half.
“This performance is not fitting of Atletico, this was not what we are about, we weren’t ourselves at any point in the game,” he told reporters.
“They were far better than us in the second half, they were superior in every aspect, you cannot explain it any other way.
“The game was a real struggle for us, they played some great football and we had some good moments in the first half but didn’t take advantage.
” We really lacked intensity in the second half, and the way we conceded the second goal was awful.”