Granit Xhaka was dismissed for violent conduct as a desperately poor Arsenal side were jeered off by their own supporters after being stunned by Premier League strugglers Burnley.
Defeat meant Mikel Arteta's side have now lost four straight league games at home for the first time in 61 years.
Gunners skipper Pierre-Emerick Aubameyang's wretched run of form continued as he failed to score at the right end - and headed an own goal at the other end.
Burnley's winner came after Xhaka was dismissed on 58 minutes for grabbing the throat of Clarets midfielder Ashley Westwood - the Swiss midfielder given a red card after referee Graham Scott reviewed the incident on the pitch-side monitor.