London: Jose Mourinho has warned his Chelsea stars they must develop a ruthless streak after the Blues fell to their first Premier League defeat since the manager`s return.
Mourinho was left to rue his team`s failure to convert chances at Goodison Park on Saturday as Steven Naismith earned Everton a 1-0 win with a goal on the stroke of half-time.
Chelsea consequently passed up the opportunity to claim top spot as Mourinho discovered there remains work to be done if he is to mark his first year back at Stamford Bridge with another title.
Samuel Eto`o, making his debut following his arrival from Russian club Anzhi Makhachkala, was particularly guilty with a series of misses -- the biggest of them a failure to convert with the goal gaping after Everton debutant Gareth Barry made a fine last-ditch tackle.
"We didn`t score goals. We had chances and didn`t score," Mourinho said.
"People with experience in football, we all know this happens week after week. If you don`t score, what you create means nothing.
"If they don`t have it (killer instinct) they have to get it. Samuel was a killer all his career. Even so the situations where he was involved in the game makes me happy."
Mourinho refused to accept a lack of sharpness on Eto`o`s part was to blame for the chances missed by the former Barcelona star.
"I don`t think it is a question of sharpness," he added. "Andre Schurrle`s pass gives time for Barry to come, if it is a fast ball, boom, Eto`o scores.
"Maybe one day we have three chances, we score three goals, we win 3-0. We had 21 shots, nine on target.
"Before they scored a goal, we had easy chances. Eto`o`s is an easy one. The other one, Schurrle over the bar is an easy one.
"Eto`o`s header is an easy one. Ramires in the second half is not a difficult one. The players are good so sooner or later we will score goals."
It was a deserved win which represented Everton boss Roberto Martinez`s first in the league since replacing David Moyes.
They remain unbeaten and, on this evidence, look capable of continuing the progress they made under Moyes.
Chelsea were left to rue their misses in added time at the end of the first half when Nikica Jelavic, at the back post, nodded Leon Osman`s clipped cross back into Naismith`s path and, with Petr Cech caught in between, Naismith, on his 27th birthday, powered home a header into the roof of the net.
More Chelsea chances went to waste after the break -- but Leighton Baines almost doubled the advantage in the closing moments with a free-kick against the crossbar.
Martinez said: "It`s difficult to describe. It wasn`t the perfect performance but we showed great character."
"The crowd understood we are still adapting and trying to play in a different manner."
"The way we defended was immense and I thought we always carried a good threat."
"It was one of those performances where I couldn`t be prouder. It gives us a great platform to become much better in what we are trying to do."