- Fidel (41')
The Croatia keeper, standing in for the injured Jan Oblak, let a long throw-in from the left touchline slip through his hands inside the six-yard box, with Elche's Fidel Chaves in the right place to tap the ball into a wide-open net in the 41st minute.
Runaway leaders Barca have 82 points and will get the chance to clinch their 27th LaLiga crown with four games to spare when they face Espanyol later on Sunday.
"In the first half we were not good, nothing came out of it," Atletico captain Koke told Movistar Plus.
"In the second half the team reacted but we were not as we should be. We have to learn from this defeat for the future. We want to be as high as possible. Hopefully we can win the last few matches."
Atletico put in a toothless performance and let Elche dominate proceedings from the beginning with almost 60% of possession in a dour first half.
After Fidel scored right before half-time, Atletico tried to show some fighting spirit and make a game of it in the second half but Yannick Carrasco and Alvaro Morata scuffed their half-chances.
It was a wake-up call for an Atletico side who have had an excellent second half of an otherwise disappointing season. They were eliminated from European competition in November after finishing last in their Champions League group, and they dropped as low as sixth in the LaLiga standings before the World Cup break.
- Alejandro Muñiz Ruiz