Song has played 20 times this season and Wenger believes the Cameroon international is getting back to his best.
"He looks extremely focused and motivated," the manager said. "I brought him here when he was not 17 years old, so I know how good he is.
"West Ham had a very strong start to the season and he was one of the influential players in there, with the strikers Diafra Sakho and Enner Valencia, and the repositioning of Stewart Downing.
"Another player I think has done extremely well is Cheikhou Kouyate. They were a very good pair in there and have given some technical quality to West Ham's side.
"We have been consistent against West Ham, especially at the Emirates. We are consistent against everybody [at Emirates Stadium] but away from home we have been successful against West Ham recently.
"When you look at the table every point is important now and our home form will be decisive as well. At the end of the day we have six home games and every game is vital now."
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