Danish midfielder Christian Eriksen was the hero as Chelsea slumped to a first defeat to Brentford since 1939.
Eriksen inspired the Bees to a 4-1 win that should seal their Premier League survival.
The European champions had gone in front early in the second half at Stamford Bridge through Antonio Rudiger’s sensational long-range strike, but they collapsed to lose for the first time since owner Roman Abramovich was hit by UK government sanctions.
Vitaly Janelt leveled just a minute later to spark a three-goal spree in 10 minutes for the visitors.
Eriksen has been in fine form since making his return to competitive football after suffering a cardiac arrest on the field during Euro 2020.
The former Tottenham midfielder scored twice in as many games during his international comeback for Denmark and continued his scoring streak by lifting the ball over Edouard Mendy to complete the turnaround.
Janelt then made it 3-1 with a deft dink over Mendy on the hour mark.
Third-placed Chelsea remains on course to finish in the top four but will need a major improvement for the visit of Real Madrid in the Champions League quarter-finals on Tuesday.
Yoann Wissa rounded off a memorable afternoon for Thomas Frank’s men when he took advantage of more comical Chelsea defending to drill home a fourth.
A third win in four games takes Brentford up to 14th and 11 points clear of the relegation zone.
At the top of the table, Man City remained one point clear of Liverpool after both teams won on Saturday; the title rivals face each other at the Etihad next Sunday.
Liverpool’s 2-0 victory over Watford in Saturday’s lunchtime kick-off moved Klopp’s side to the summit for a few hours before City beat Burnley 2-0 to reclaim the top spot and remain a point clear.
City and Liverpool were neck and neck in a similar fashion in the 2018/19 season as both teams put together winning runs before Guardiola’s side clinched the title by a point on the final day.
Meanwhile, Cristiano Ronaldo missed Manchester United’s disappointing 1-1 draw against Leicester City on Saturday afternoon through an unspecified illness.
United struggled without their Portuguese star – who made it six Premier League games without starting since returning to Old Trafford in the summer – continued as they scrapped out a fortuitous stalemate with the Foxes.
Interim boss Ralf Rangnick confirmed the Portuguese was unavailable through illness, saying before the game: ‘He had some flu-like symptoms yesterday (Friday).’
And his presence and match-winning potential were missed, with the hosts only managing a draw after Fred canceled out Kelechi Iheanacho’s opener.
Ronaldo has scored 18 goals in 33 appearances in all competitions for United this season and netted a hat-trick in his side’s 3-2 win against Tottenham just before the international break.
The 37-year-old played in both playoffs ties over the past two weeks as Portugal secured a place at the 2022 World Cup, which will mark his fifth appearance at the tournament – equalling a record held by Lothar Matthaus, Rafa Marquez, and Gianluigi Buffon.
Edinson Cavani was also unavailable for United, after picking up a knock while on international duty with Uruguay.
The return of Ralf Rangnick’s men to Premier League action for the first time since March 12 however saw them blow the chance of leapfrogging Tottenham and closing the gap to fourth-place Arsenal to a single point.
Wolves are up to seventh in the Premier League after a hard-fought win over Steven Gerrard’s Aston Villa.
The hosts boosted their hopes of European football next season thanks to an early goal from Jonny before an Ashley Young own-goal doubled their lead.
Ollie Watkins missed two chances to put his side back in it and it was too late little too late when he finally scored four minutes from time with a well-struck penalty.
Wolves leapfrogged West Ham with their third win in seven games and are just two points adrift of Manchester United.
A seventh-place finish will likely see them qualify for next season’s Europa Conference League.
Elsewhere, Neal Maupay missed a 29th-minute penalty in a drab stalemate between Brighton and Norwich.
Maupay had a golden opportunity to give his side the lead after Sam Byram’s handball inside the box saw the Seagulls awarded a penalty.
But Maupay blasted his effort over the bar.
Joel Veltman also came close for the hosts but his headed effort from point-blank range was brilliantly blocked by countryman Tim Krul.
And thanks to Krul the Canaries ended their run of six consecutive league defeats.
Leeds and Southampton also shared the points on Saturday.
Jack Harrison’s close-range finish inside 30 minutes gave Leeds the lead but James Ward-Prowse’s brilliant free-kick denied the Whites a third consecutive league win.
He has now scored three times from a direct free-kick this season, just one short of his overall tally from last season.