Chelsea did their best to launch a positive response, but the Blues were struggling, and Burnley incredibly doubled their lead in the 39th minute when Stephen Ward broke into the home side's box before finding the top corner with a stunning strike.
It began to unravel before the quarter-hour mark when Cahill was shown a straight red card for his lunge at Defour before Fabregas was booked for sarcastically clapping Pawson.
Antonio Conte was facing a full-blown crisis on Saturday night after his Chelsea side were embarrassed by Burnley's shock 3-2 victory at Stamford Bridge.
Two years ago, Chelsea drew with Swansea 2-2 at home in the first match of its league title defense and quickly unraveled.
Burnley's win, their first at Chelsea since 1971, further blackened the mood around Stamford Bridge after a close season during which Conte has grown frustrated by his club's lack of transfer activity.
New signing Alvaro Morata from Real Madrid came on to pull one back midway through the second half and then provided an assist for David Luiz, but in-between midfielder Cesc Fabregas was also sent off for a second yellow card.
After the opening game of the season on Friday produced seven goals and a late victor for Arsenal, who beat Leicester City 4-3, the two teams at Vicarage Road served up more of the same entertainment for a worldwide television audience - including some poor defending.
Conte said he did not want to answer questions about Costa, but tellingly conceded: "For me it's in the past".
He brushed aside questions about reported tension with Chelsea's board over signing new players and said he was not anxious because three key players - Eden Hazard, Pedro and Victor Moses - could return from injury and suspension for Chelsea's next game against London rivals Tottenham Hotspur at Wembley.
Despite his criticism, Rudiger believes Chelsea's attempt to salvage a point against the odds should give them encouragement that the defeat is only a temporary blip. In pre-season, in every friendly game I played the best formation and it happened also today. "No, if we're honest", said Burnley manager Sean Dyche.
"We still gave away possession too easily in the second half". Why do I have to send a message? "This win won't do us any harm at all but it won't make our season".
Egyptian defender Ahmed Hegazi, on loan to West Bromwich Albion from Al Ahly, scored on his debut in the 1-0 win at home to Bournemouth.