The £12 million summer signing from Montpellier had struggled to get off the mark for the Gunners in the league but struck the crucial equaliser that set Arsene Wengers’ side on the way to victory.
Sam Allardyce will be disappointed that his side failed to build on an impressive win against QPR on Monday after taking a surprise 21st minute lead through Mohamed Diame.
The Hammers, including Andy Carroll for the first time since his debut against Swansea last month, were forced to defend for much of the first half with the on-loan Liverpool striker proving his worth blocking a Giroud effort just moments after the Arsenal striker saw Jussi Jaaskelainen tip his second minute shot round the post.
Diame took advantage of the visitors’ wastefulness in front of goal, stepping inside Aaron Ramsey and curling a wonderful finish past Vito Mannone for his first goal for the club since joining from Wigan.
Diame’s celebrations were short lived as his surrendering of possession in midfield led to Arsenal’s equaliser five minutes before half time. The ball was pushed out wide to Lukas Podolski and his cross was clinically turned home at the near post by the on rushing Giroud to the visible joy of Wenger
West Ham went close twice to retaking the lead through Carroll and captain Kevin Nolan before Theo Walcott came off the bench to put Arsenal in front, latching on to Giroud’s through ball and cooly finished past Jaaskelainen with 13 minutes remaining.
Another costly miss from Nolan was punished by Santi Cazorla as the Spaniard lashed home a magnificent 20-yard strike to cap a superb individual performance.