An Arsenal football supporter has been arrested on suspicion of common assault and pitch invasion, after running onto the field and shoving Manchester United defender Chris Smalling.
The incident happened shortly after Arsenal striker Pierre-Emerick Aubameyang scored a spot-kick in the 69th minute to give the Gunners a 2-0 lead.
After taunting and pushing Smalling, the fan ran with his arms in the air towards Arsenal players celebrating the goal.
Smalling was not hurt and Arsenal stewards took the man off the pitch.
"A man has been arrested on suspicion of common assault and pitch invasion, following an incident during the Arsenal vs Man Utd game at the Emirates Stadium today," local police later confirmed.
"He is currently in custody at a north London police station."
Commentator and former Manchester United defender Gary Neville called the fan an "absolute numpty".
Arsenal went onto win the match 2-0, as Unai Emery's side inflicted the first league defeat of Ole Gunnar Solskjaer's United tenure.
The incident occurred hours after a Birmingham fan ran onto the field and punched Aston Villa captain Jack Grealish during their local derby.
Grealish went onto score the match-winning goal in that match, while Villa leapfrogged Birmingham in the Championship standings.
The win lifted Arsenal to 60 points, just one point behind north London rivals Tottenham Hotspur, who are third, and two points above United, who slipped to fifth.
Earlier, Liverpool beat Chris Wood's Burnley 4-2 to keep the pressure on leaders Manchester City.
Forwards Roberto Firmino and Sadio Mane both scored doubles against Burnley, while Ashley Westwood and Johann Berg Gudmundsson scored for the Clarets.
Liverpool now trail City by one point, while Burnley remain two points above the relegation zone.
Meanwhile, Eden Hazard scored in stoppage time to help Chelsea draw 1-1 against Wolverhampton Wanderers at Stamford Bridge.