It is likely to be his final appearance for the club, despite fixtures against Eintracht Frankfurt and Leicester to come this week and a potential Europa League final.
During his time at Chelsea he has won the Champions League, Premier League, Europa League, FA Cup and League Cup, and he told the club's official website: "It was a great moment for me to get out there and say goodbye and just thank the supporters for the great career I have had here of mostly ups. It has been fantastic.
"The Champions League in Munich was an amazing night to be part of, to be in the team that enabled Chelsea to win it for the first time was amazing but a very close second for me was the first Premier League I won.
Top 50 most valuable Under-20 players
Show all 51
"I have watched this league since I was a kid and I know how hard it is to go out every single week and try to get three points, as you saw in this game in the first half against Watford, so to do that consistently throughout the period of a season and to win the trophy is one of the best feelings as well."
Former Chelsea midfielder Nathaniel Chalobah was also handed a rare appearance by visitors Watford, making his first league start since December.
His manager Javi Gracia had been impressed with his performance during the first half and Chalobah told Watford's official website: "It's been a very difficult year for me, coming in and out, but I just tried to give everything I can.
Cahill applauds the Chelsea fans
(EPA)
"I left it all out there and I blew up after about 50 minutes! It's always difficult not playing games and that match fitness and sharpness is something you always lack when you don't get that opportunity.
"But what can I do? The boys been flying this year and you've got to look at it that way and keep going."
PA Sport also contributed to this report
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies