Arsenal interim boss Freddie Ljungberg told BBC Sport: "The players have belief and tried to move the ball with more tempo. West Ham got tired.
"The players ran their socks off and fought. I believe in them. When I could see them put their shift in, I could see the quality. I thought 'it is here for the taking'.
"Martinelli did amazingly. He is like a Duracell battery, he keeps going. Laca [Alexandre Lacazette] is a tremendous player but I had to make a tough decision."
West Ham manager Manuel Pellegrini told BBC Sport: "For 60 minutes there was just one team on the pitch. But football can be like this.
"We made mistakes in moments of defending. The problem was a lack of patience and quality to decide the game with a second goal and we made important mistakes in defence.
"The pressure for me is exactly the same if we win or lose. When you don't have results things are more difficult. If I had not seen the team play the way they did in the first 65 minutes, I might have doubts [about his ability to turn things around].
"After Southampton at the weekend we have a break. We must try to recover as quickly as we can and we must try to win those three points."