Chelsea slumped to another damaging home defeat against Brentford on Saturday as Eddie Nketiah hit a first Premier League hat-trick in a 5-0 win for Arsenal against struggling Sheffield United.
Mauricio Pochettino's Chelsea appeared to have turned a corner in recent weeks, taking seven points from their three previous fixtures, but their 2-0 loss means they have just one home win from their past 13 games in the league.
Ethan Pinnock took advantage of non-existent marking to head the visitors in front shortly before the hour mark at Stamford Bridge after Chelsea had failed to capitalise on their first-half dominance.
Goalkeeper Robert Sanchez was embarrassed in added time after joining his team's attack for a corner, failing to catch Neal Maupay in a race as he broke with the ball, allowing Bryan Mbeumo to score in an empty net to compound home fans' woes.
The result means Brentford leapfrog Chelsea into 10th place in the Premier League table, pushing Pochettino's men into the bottom half.
"I'm not happy and think the players also and the whole club is not happy about the run (at home)," said the Argentine manager.
"It's a long time that we need to be more consistent here and very disappointed with this. We feel the responsibility that we need to change the dynamic."
The former Tottenham boss said on Friday that Christopher Nkunku is nearing a comeback from the knee injury that has prevented the £52 million ($63 million) signing making a competitive appearance yet for his new club.
On this evidence, the French international's return cannot come soon enough as Chelsea's other new striker, Nicolas Jackson, again failed to fire.
"If you don't score, you need to blame ourselves," said Pochettino. "We were not nasty or clinical in front of the goal."
- Nketiah hat-trick -
It was a different story for London rivals Arsenal, who roared back from 2-0 down to draw against Chelsea last week to preserve their unbeaten league record.
Arsenal boss Mikel Arteta shuffled his pack --including dropping captain Martin Odegaard to the bench -- for the visit of bottom club Sheffield United and Nketiah celebrated his recall to the starting line-up in style.
Replacing the injured Gabriel Jesus as Arsenal's target man at the Emirates Stadium, Nketiah proved he was up to the task as a swivelled finish gave the home side a 28th-minute lead.
The England forward arrowed a shot into the top corner early in the second half and completed his treble with a stunning strike from distance just before the hour mark.
Substitutes Fabio Vieira and Takehiro Tomiyasu added gloss to the scoreline with a penalty and a close-range finish as Arsenal moved up to second in the table, two points behind Tottenham, who beat Crystal Palace on Friday.
"It's amazing," said Nketiah. "It's not been easy -- last month I lost my auntie so I want to dedicate these three goals to her. Her family was here watching so it is a really special moment."
Bournemouth came from behind to beat fellow strugglers Burnley 2-1 and secure their first league win of the season thanks to a fine solo effort from Antoine Semenyo and a sensational lob from distance by Philip Billing late in the game.
Newcastle, who have won four of their past five league games, take on Wolves in the late kick-off.
High-flying Liverpool host Nottingham Forest on Sunday while champions Manchester City make the short journey to face Manchester United at Old Trafford.
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