Chelsea midfielder Moises Caicedo was sent off in the 38th minute at Stamford Bridge for a crude foul on Merino that caught the midfielder on his ankle.

Despite Caicedo's dismissal, Trevoh Chalobah headed Chelsea from Reece James' corner into the lead in the 48th minute.

But Merino's close-range header from Bukayo Saka's cross in the 59th minute ensured Arsenal emerged unscathed from a bruising encounter between the title rivals.

Arsenal are five points clear of second-placed Manchester City, who beat Newcastle on Saturday, and sit six points above third-placed Chelsea.

The Gunners remain the favourites to win their first Premier League crown since 2004, but Chelsea's combative display suggested they could emerge as the biggest threat to the Gunners' title aspirations.

Arsenal are unbeaten in 17 games in all competitions, winning 14 of those matches, while Chelsea have gone seven matches without losing in all competitions.