The Gunners had been knocked out of the last Champions League qualification spot by north London rivals Tottenham Hotspur earlier on Monday (NZ time) after they beat Leicester City.
Son Heung-min struck twice after Harry Kane had opened the scoring as Spurs bagged a 3-1 at home.
But Arsenal responded to the pressure with a third consecutive victory to give them the edge in what has become a two-horse race for fourth place.
Arsenal have 63 points from 34 games with Tottenham on 61 points, also with four games left to play.
Elsewhere Striker Richardson profited from a Chelsea error to secure struggling Everton a 1-0 win and what could be a precious three points in their bid to avoid relegation at a rocking Goodison Park.
Chelsea remain third with 66 points from 34 games as they also bid to qualify for the Champions League.