London - Maurizio Sarri warned his Chelsea stars to improve their mentality after Willian's sublime strike sealed a hard-fought 2-1 win over struggling Newcastle on Saturday.
Sarri's side took the lead through Pedro's early goal, but Ciaran Clark snatched a shock equaliser before half-time.
With Chelsea fans beginning to lose patience at their team's latest spluttering home display, Willian lifted the mood in the nick of time with his superb second-half curler.
Fourth-placed Chelsea have won five of their last seven league matches and sit six points clear of fifth-placed Arsenal, who lost at West Ham earlier on Saturday.
But, while Chelsea remain in control of the race to qualify for the Champions League, this was a far from convincing performance.
Labouring to beat third-bottom Newcastle showed how far Chelsea have to go to bridge the gap in class to leaders Liverpool and champions Manchester City.
Sarri admitted he was frustrated with the way Chelsea took their foot off the gas after the opening goal.
"We started well for 10 minutes but after the goal we thought 'now it is easy', but it wasn't," Sarri said.
"We slept for 25 minutes and then we were in trouble. We were better in the second half but we need to improve the mental reaction.
"It is very difficult to understand. We stopped playing and then we had problems."
Sarri also revealed he has told Chelsea's hierarchy he needs a new midfielder to replace Cesc Fabregas, who joined Monaco on Friday.
"Jorginho was in trouble and on the bench there wasn't a player for that position. I need an option for that position," he said.
"The club knows very well my opinion. It depends on the club decision. I cannot do anything more."
Another winter of discontent is brewing for Newcastle, wo have won only once in their last nine league games.
The Magpies' 18 points is their lowest tally after 22 matches of a top-flight season since they were relegated in 1988-89.
"We have to be better than three teams and if we play like today we can do it," Benitez said of Newcastle's relegation battle.
Tuesday's 1-0 defeat against Tottenham in the League Cup semi-final first leg was the latest display of attacking impotence from misfiring Chelsea, who had failed to score in their last two home league games.
But it took only nine minutes for the Blues to go in front as Newcastle's five-man defence was carved open with ease.
A fine long pass from Chelsea defender David Luiz caught Clark flat-footed.
Pedro timed his run behind Clark perfectly and held off the centre-back's weak attempt to recover as he lofted a delicate chip over Newcastle keeper Martin Dubravka for his seventh goal of the season.
Chelsea dominated possession in the first half-hour, but they switched off at the back as Newcastle almost snatched an equaliser.
Salomon Rondon flicked a header towards Ayoze Perez and he accelerated away from Antonio Rudiger, only to shoot woefully wide with just Kepa Arrizabalaga to beat.
It was a warning that Sarri's men failed to heed and in the 40th minute Newcastle were level.
Matt Ritchie curled over an out-swinging corner and Clark muscled past Luiz to power a superb header past Kepa from 12 yards.
Once again, Sarri stubbornly stuck to his experiment with Eden Hazard as Chelsea's central striker despite the Belgian star's dislike of the tactic.
Hazard has now scored just four times in his last 17 games, suggesting he is much more effective in his natural role on the flanks.
With frustration mounting, a misplaced pass by Jorginho triggered angry moans from Chelsea fans, who booed the team off at half-time.
The atmosphere was on the verge of turning even more toxic until Willian came to the rescue in the 57th minute.
Teed up by Hazard at last making an incisive burst, Willian cut back inside two Newcastle defenders on the left side of the area before curling a masterful finish into the far corner.