Sam Allardyce turned to the on-loan Barcelona midfielder to lead out his side for the London derby, as Kevin Nolan started on the bench and vice-captain Mark Noble was ruled out due to injury.
Song led by example as West Ham secured their third Premier League victory of the season to move up to seventh place and the Cameroon international welcomed the responsibility of skippering the side.
"I have been captain before at Arsenal but it was a privilege to wear the armband against QPR," he told the club's official website.
"I know Kevin Nolan and Mark Noble have been captains this season but without them, the manager had to choose someone and it was good he showed the trust in me. I just wanted to return that faith and thank him for that responsibility."
Song also revealed that his cousin, Rigobert Song, played a big part in convincing him to move to Upton Park, having spent a spell with West Ham during his playing days.
"I spoke to him very recently," he said. "He has helped me a lot with my decision to come here.
"He told me it was a good club and the fans were terrific. After I came here I told him he was right about that."
The combative Song has been buoyed by West Ham's start to the season and believes a top-10 finish would represent a good achievement.
"We have some players injured and others who are coming back after being out for a long time. When we have them all back we will be even stronger and you never know what might happen.
"We are seventh at the moment but I am not going to put pressure on us by saying we will end up there. If we finish in the top 10 it will be fantastic but we must stay focused and give everything in every game to do that."
West Ham travel to Burnley in their next game after the international break a week on Saturday.
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