Powerhouse Tykes striker Kayode Odejayi delivered the holders a sensational knockout blow, rising highest to head home Martin Devaney's superb cross in the 65th minute for the only goal in a thrilling 'David versus Goliath' quarter-final at a sold-out Oakwell.

Chelsea manager Avram Grant conceded it was his worst day since replacing Jose Mourinho 37 games and only four defeats ago.

But the Israeli and his captain were gracious enough in defeat to pay tribute to Coca-Cola Championship side Barnsley and their fairytale cup run. Davey said of his opposite number: "He just said 'well done'. He was very sociable. He's a nice fella.

"John Terry came up to me at the end of the game and said 'go on and win it, you deserve it after today'.

"So it's great to have people of that stature in the game saying that afterwards."

Davey, who never played above League One level as a player, admitted he and his players were in "dreamland" after trumping their memorable win at Liverpool in the previous round.

"I never thought the Anfield win could be eclipsed and today, in front of our own fans, against mighty Chelsea with all their millions, we've done it and I couldn't believe it.

"I still can't believe it now and hopefully I'll wake up in the morning and it will still all be true."

Barnsley went toe to toe with Chelsea in a typically full-blooded cup tie and even played some of the better football in the first half.

Chelsea a took command early in the second half and it appeared their extra class would tell, but just when Barnsley legs appeared to waver, Delaney swung over a top-class cross and Odejayi thumped home his decisive header.

Davey added: "You have to enjoy days like these. It was a big day for Barnsley and a big day for the players and they went out to enjoy the game.

"Nobody was found wanting. Everyone put a shift in and they've come up trumps again.

"To go to Anfield and win and then to go and beat Chelsea in the same season is a fantastic achievement and my players deserve a lot of praise."

Davey revealed his most expensive player was Hungarian striker Istvan Ferenczi, who cost a tiny fraction of the £110million it cost Chelsea owner Roman Abramovich to assemble the Londoners' side on show at Oakwell.

But it was match-winner Odejayi, who scored his first goal since September, that Davey singled out for special praise.

Davey said: "My players, last-ditch tackles, Luke (Steele) again pulling off saves - they've been fantastic.

"But a lot of the credit for me has got to go to 'Kay'. He has been fantastic all season. He got a bit of criticism earlier, but we know he's a good player and that he'd come good.

"Over the last month he's put a lot of hard work in and he's had his reward today."

Chelsea manager Grant, who insisted both Frank Lampard and Didier Drogba were left out due to injury, looked drawn when asked to assess his side's upset.

He also laid some of the blame on the Oakwell pitch, and said: "It's a big disappointment. It's a quarter-final and we lost.

"First of all I need to congratulate Barnsley. They played very well today and showed good spirit.

"For us it's not a pitch we can play quality football on. It was not good in the first half and the second half we started very well.

"We played quick, we created a lot of chances and then, like it happens sometimes in football, we conceded a goal and we couldn't score.

"I don't think we thought this was an easy game. We knew they beat Liverpool away, so we knew what to expect.

"I wanted both (Lampard and Drogba) to play, but they were injured, so they couldn't, but we played with a team that was good enough to win the game."

Grant added: "I don't know if I'm shocked, but I'm very disappointed. You can say so yes, since I came to Chelsea, this is the most disappointing day."