Chelsea boss Maurizio Sarri said he could not explain the second-half performance of his team after they collapsed to a 2-0 defeat against Everton at Goodison Park.
The Blues missed the chance to move level on points with fourth-placed Arsenal and instead remain sixth as they threw away their game in hand.
It was a Jekyll and Hyde performance that saw them have a firm grip of the contest in the first-half only to be outplayed after the break.
Everton striker Richarlison set the tone for a chastening second-half for the visitors with his 13th goal of the season just after the restart before Gylfi Sigurdsson added a second midway through the half.
Sarri said: “I don’t know and the players don’t know what happened in the second half. I cannot explain it.
“We played the best first half in the season and we could have scored four or five and then suddenly we stopped playing. It’s very strange and we stopped to defend and counter-attack.
“We were in control of the match and we played very well so we needed continue but we didn’t defend at the start of the second half. We changed the system but it was the same.
“The problem was mental on the pitch, so the system and the tactics are not important. It wasn’t about motivation because we started very well. We have to play eight matches now and we have to fight for our possibilities.”
Chelsea could have been out of sight in the early stages but failed to get the breakthrough their play warranted.
Belgian playmaker Eden Hazard forced England keeper Jordan Pickford into a reaction save at his near post and a minute later struck the far post with the aid of a Andre Gomes deflection.
Pickford was again called into action to deny Gonzalo Higuain as the Everton rearguard were living on their nerve
The home side took 37 minutes to have a touch in the Chelsea box but looked a different side after the break with Richarlison opening the scoring with a downward header after Kepa had blocked a Calvert-Lewin effort from a corner.
Chelsea lacked a cutting edge and were picked off again with Gylfi Sigurdsson doubling the Toffees’ lead when he pounced on the rebound after his penalty was saved by Kepa.
Everton threw away a two-goal lead against Newcastle last week but not this time. Indeed, substitute Theo Walcott almost added a third but Kepa got down smartly to keep out his angled drive from a Sigurdsson threaded pass.
This was Everton’s first win against a top-six side in 28 attempts stretching back to the 4-0 victory over Pep Guardiola’s Manchester City in January 2017. It moved them above Bournemouth into 11th and was undoubtedly Marco Silva’s best day as Everton boss.
“The frustrating thing this season has been being consistent,” said Everton and Ireland full-back Seamus Coleman. “That is the next step for us. We want to be challenging in the top six in the future but we know we have been miles off.”