On 26 July 2017, Cahill was appointed as the Chelsea club captain ahead of the 2017–18 season, following John Terry's departure. On 12 August 2017, in the first match of Chelsea's 2017–18 season against Burnley at Stamford Bridge, Cahill was sent off in the 13th minute of the match for a reckless studs-up challenge on Burnley midfielder Steven Defour, culminating in a sequence of events that saw Chelsea begin their title defence with a shock 3–2 defeat to a Burnley team that had only won once away from home in the previous season. Cahill was suspended for Chelsea's league matches against rivals Tottenham Hotspur, Everton and Leicester City. He captained Chelsea to victory at Wembley Stadium in the 2018 FA Cup Final, his team beating Manchester United 1–0.