The 'Help' star, 26, took over the roll from Michelle Williams, performing alongside Alan Cumming, reported Us magazine.
"Andrew came sharply dressed in a suit. Andrew came backstage after the show with Emma's mother and his guests. He kissed her and congratulated her," a source said.
The couple, who met on the set of 'The Amazing Spider-Man', began dating in the summer of 2011. Since then they have attended numerous events together, but mostly keeping their personal life private.
The 'Social Network' actor, 31, had his own time to shine on Broadway in 2012 when he appeared in the revival of Arthur Miller's 'Death of a Salesman' alongside the late Philip Seymour Hoffman. His performance as Biff earned him a Tony Award nomination.