"We scored three good goals and I think when you are talking about who you are playing against and where you are playing, that's up there as one of the best 45 minutes of my time here", said the manager, who joined Burnley in 2012.
Morata make his presence felt straightaway, getting Chelsea's first goal of the afternoon before teeing up David Luiz for the second.
He added: "We have to think that there is the rest of the game to play and do our best".
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. "In the second half, my players showed great will to try to change the result".
The Blues were unable to respond to a straight red for Cahill in the early stages, with Sam Vokes then recording a brace either side of Stephen Ward's rocket before half-time. "You can see that in every friendly game I always played the best formation and I did the same today".
Chelsea are only the second reigning Premier League champions to have lost their opening game of the following season, after Leicester lost 2-1 to Hull City in their first match of the 2016/17 campaign.
"It's a great win for us, brilliant for our players, brilliant for our supporters but we know there's a big season right in front of us, the "second season" that everyone's telling us about".
"From there, it is very hard to change the result".
"At 3-0 up we should have made it safer, but we got there in the end".
He said: "We just lost our heads". Chelsea are a top-class side and it is tough to come here and dominant possession, even when they have 10 men, but we were too flippant with the ball and we gave it away too cheaply.
"To start the season with two red cards and a bad result is not good", admitted new defender Antonio Rudiger.
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