Chelsea boss Maurizio Sarri says he is baffled by his side's second half performance at Goodison Park after they slumped to a 2-0 defeat to damage their top four Premier League hopes.
The opening 45 minutes saw neither side able to break the deadlock, but the story was different after the break as Everton emerged a different team.
The Toffees took the lead within four minutes of the restart when Richarlison headed them ahead.
Richarlison took full advantage of Chelsea goalkeeper Kepa parrying out a header from Dominic Calvert-Lewin, which went into his path.
Everton's second arrived in the 72nd minute with Gylfi Sigurdsson scoring at the second attempt after he had a penalty saved by Kepa.
Marcos Alonso conceded the penalty, fouling Richarlison.
And it ended 2-0 to the Toffees, a result which means Chelsea remain three points behind fourth placed Arsenal, sitting in sixth.
Sarri feels his side could have scored four in the first half, but then their performance dipped in the second period and the Italian admits he is at a loss to explain why.
"I don't know and the players don't know what happened in the second half. I cannot explain it", Sarri told Sky Sports after the game.
"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."
Sarri is now keen for his men to look forward and seek to win their last eight games.
"We have to play eight matches now and we have to fight for our possibilities."
