LaLiga giants Atletico Madrid were held to a 1-1 draw in the away first leg of their last-32 Copa del Rey tie with third-tier Elche on Wednesday.
Diego Simeone rested stars including Antoine Griezmann, Koke, Jan Oblak and Diego Godin ahead of Saturday's league game against Villarreal and his replacements failed to get the job done.
Atletico started well, however, and took only 17 minutes to break the deadlock, Thomas Partey beating goalkeeper Guillermo Vallejo with a fine header after the midfielder was picked out at the back post by Jose Gimenez.
The visitors, who benched Saul Niguez against the Spain international's hometown team, wasted many opportunities to extend their lead and Elche promptly levelled shortly after half-time, Lolo Pla converting a penalty he won himself by drawing a foul from Lucas Hernandez.
Luciano Vietto's finishing was particularly poor, the forward hitting the post with a fine first-half chance, and hosts Elche could even have won it after building sustained pressure late in the match.
Elche had lost their last two league games but Vicente Mir's team will travel to the Wanda Metropolitano next month seeking another famous result.
Despite making nine changes from their 1-0 win at Celta Vigo last time out, Atletico went close to opening the scoring almost immediately, but Sime Vrsaljko's fizzing right-wing cross was turned wide of the near post by Fernando Torres.
Nicolas Gaitan then whipped a shot just over the angle after great work from Vietto set up debutant Sergio Gonzalez to deliver a low cross.
But Elche could not keep Atleti out much longer and the opener duly arrived.
After Elche failed to clear their lines, Gimenez delivered a sublime cross to the back post, with Thomas' header bouncing into the ground and into Vallejo's top-right corner.
The hosts responded strongly, though, and Miguel Angel Moya had to dive to his left to keep out a drive from Javi Flores after Pla's neat backheel created an opening.
Vietto went close to adding to Atletico's lead when he struck the foot of the post after racing on to a loose Elche pass, before Vallejo brilliantly saved a header from Torres shortly before half time.
And all those wasted chances proved costly when Elche scored a penalty seven minutes after the restart, which was awarded after Hernandez lunged in from behind to stop Pla's brilliant 30-yard driving run.
Pla confidently sent Moya the wrong way from the spot to level the tie but he then limped off with an injury, while Simeone called for Saul, who had been presented with an Elche shirt on the pitch before the game.
Torres sent Vietto through again just after the hour mark, but the striker, who could have had a hat-trick, sent his chipped finish wide.
It was then Elche who dominated the rest of the contest, with Atletico unable to make the gulf in class between the sides count, and Simeone's men will need to be better in next month's second leg to avoid an upset.