Olivier Giroud came off the bench to rescue a point with a late goal at Old Trafford.
The Frenchman soared about the Manchester United defence to thump a header past David De Gea after a fine cross from another substitute, Alex Oxlade-Chamberlain.
Juan Mata looked to have condemned the Gunners to defeat with an unerring first-time finish from Ander Herrera’s cut-back - and for a long while this rather flat game looked like a missed opportunity.
Giroud and Oxlade-Chamberlain changed all that, and Arsenal will head home on a relative high despite missing the chance to go top of the Premier League.