The champions suffered their first opening-day loss for 19 years after failing to recover from a first half that saw Gary Cahill sent off before Burnley raced into a three-goal lead, courtesy of Sam Vokes' double and a superb Stephen Ward strike.
No one would believe that Burnley would provide such an astonishing performance at Stamford Bridge as many Chelsea fans left the Stadium livid. I'm not anxious because we have to trust in our work and today there were three injured players, Pedro, Hazard, Bakayoko, and one player missing for a ban, [Victor] Moses.
"Instead we conceded three goals and the second half was very hard to change the result, despite the great commitment, the great desire, the great will of my players".
Romelu Lukaku is a very good signing and Nemanja Matic is a brilliant pick-up from Chelsea.
Crespo who won the English Premier League title in 2006 during his brief two year stint at Chelsea, Ubelieves the Blues will face difficulty retaining the EPL title this season.
"We must pay attention and try to keep our heads the rest of the game.
I have only played two preseason games, 15 official minutes and a missed penalty", he said.
Burnley made it 3-0 before half-time when Vokes headed in Defour's free-kick.
The champions were looking much more of a threat and had the ball in the net again six minutes later but Morata who poked in Andreas Christensen's shot at the far post was ruled offside.
Wayne Rooney crowned his first appearance for formative club Everton since 2004 by notching the victor in a 1-0 win over Stoke City, heading in Dominic Calvert-Lewin's cross for his 199th Premier League goal.
Huddersfield Town - Aaron Mooy has been one of its big signings and he was terrific last season, but it's going to be a tough one in the Premier League for it. Make no mistake, for teams like Huddersfield success is staying up.
Elsewhere on the south coast Southampton and Swansea played out a scoreless draw.