Walcott, who has yet to sign a new deal with the club and has made it clear he wants to play as a central striker, was introduced in the second half and slotted home the goal that put the Gunners ahead for the first time.
"He is slowly getting there," Wenger said. "You're confident now when he gets in front of goal that he will score. Of course he scored an important one today at a moment where the game was a bit 50-50. Theo has an outstanding attitude and I don't rule anybody out. If I did then I would not bring him on in a crucial moment in the game. I believe in him."
He added: "Gervinho looked a bit tired and Theo made the difference. He scored the second goal and that is the most important one."
Mohamed Diame opened the scoring for the home side before Olivier Giroud grabbed his first league goal for the Gunners to take the sides in level at the break.
Walcott then added the second before Santi Cazorla, who had an impeccable game for the Gunners, bent in a spectacular third. Wenger was pleased with the performance of the Spain playmaker, who moved to the Emirates from Malaga during the summer.
"I think he was overall a delight to watch," he said. "From the first to the last minute today. He was very influential in our team and it's fantastic to watch him play."
West Ham provided a stern test for Arsenal with Andy Carroll returning to the starting line-up following a hamstring injury and he caused several aerial problems for the visitors.
Hammers boss Sam Allardyce revealed he did not envisage playing Carroll for the full 90 minutes as he continues to find his fitness following his lay-off. But injuries to Guy Demel and Ricardo Vaz Te, with the latter missing for up to 12 weeks with a dislocated shoulder, meant Allardyce had no choice but to keep Carroll on.
"He is okay, he is fine," he said. "We didn't want to play him for 90 minutes because he has only just come back from that long spell injured and hasn't played that much - but unfortunately our injury plight continued as the game progressed."
Source: PA
Source: PA