- Antonio Rüdiger (48')
- Vitaly Janelt (50', 60')
- Christian Eriksen (54')
- Yoane Wissa (87')
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Eriksen then slotted home with cool finish from a low cross to put Brentford in front, adding to his fine form after scoring for Denmark on his return to the Parken Stadium on Tuesday, where he almost died of a heart attack at Euro 2020 last June.
"It's an ongoing fairytale and I am very pleased for that of course," Frank, who is also Danish, told reporters.
Janelt, who signed a new four-year deal at Brentford on Friday, added his second minutes later with a delightful chip over Chelsea goalkeeper Edouard Mendy before striker Yoane Wissa's drilled effort capped a remarkable win for the visitors.
Chelsea, who had not lost in the Premier League since mid-January, remain third in the table but lost ground on leaders Manchester City and Liverpool who both won on Saturday. Brentford moved up to 14th, four places above the drop zone.
"After so many wins and so many good results, I refuse to make a drama out of it," Chelsea boss Thomas Tuchel told reporters.
"We will find out, analyse and then we will digest it because there's no other way. It's hard to take because it's very unusual for us what happened today, and then we will refocus on Monday."
He also said he thought the game would prove to be a blip and did not represent a bad omen for Chelsea's Champions League quarterfinal against Real Madrid on Wednesday.
Frank added: "Winning here at Stamford Bridge against the European champions, and the world champions, in almost a complete performance, that's a little bit unreal."
Prior to kick-off, a small number of Chelsea fans staged a protest outside Stamford Bridge against the Ricketts bid to buy the club due to past anti-Islamic comments made by the family's patriarch, Joe Ricketts, who has since apologised.
Groups led by Martin Broughton and Todd Boehly are among the other bidders included on a shortlist of potential buyers.
- Andy Madley
|Brighton & Hove Albion||14||6||4||4||+4||22|
|West Ham United||14||6||3||5||0||21|