 During a pre-season friendly against Rotherham United, on 21 July 2012, Mellis scored the first goal in the New York Stadium since its opening on 12 March 2012.Mellis made his Barnsley debut since joining the club permanently, where he set up a goal for John Stones, in the first round of League Cup, and played 120 minutes in a 4–3 win over Rochdale.Seven days later, Mellis made his league debut in the opening game of the season, in a 1–0 win over Middlesbrough.