Arsenal interim manager, Freddie Ljunberg, told his players to play with a higher tempo, after a poor first-half performance against West Ham.
The Gunners went in 1-0 down at the break, thanks to Angelo Ogbonna's deflected header.
But Gabriel Martinelli fired Arsenal level, before Nicolas Pepe and Pierre-Emerick Aubameyang added more goals.
"We feel good. I think we played well in the second half so we are happy to win this game," Aubameyang told Sky Sports.
"We tried to put some tempo in the game and to play fast and find spaces, and we did that.
"At half-time, Freddie [Ljunberg] told us to play with a higher tempo. It was tough but we have the quality in the squad, and if we believe in ourselves, we can go forward and win games.
"We will take this second half as an example for the rest of the season."