It was a big blow to Chelsea, but they dealt with it well and got themselves in front just after half-time when Trevoh Chalobah flicked on Reece James' corner and his header looped over everyone and into the far corner.
Arsenal hit back quickly, however, and got back on level terms when Merino rose to power Bukayo Saka's cross past Robert Sanchez, and you felt at that point the visitors would go on to make their extra man advantage count.
But they struggled to create any clear cut chances and had to settle for a point which keeps them six points clear of the Blues and moved them five clear of second-placed Manchester City.
GOAL rates Arsenal's players from Stamford Bridge...






