Marin made his competitive debut for Chelsea in a League Cup match against Wolverhampton Wanderers on 25 September, coming on as a substitute as Chelsea cruised to a 6–0 victory. He made his Premier League debut on 28 November, replacing Eden Hazard in the 82nd minute of a 0–0 draw in the West London derby at home to Fulham. On 2 January 2013, Marin made his first start for Chelsea in a 0–1 loss to local rivals Queens Park Rangers. On 9 February 2013, Marin scored his first Premier League goal for Chelsea, coming on in the 91st minute and scoring on his first touch with a header in the 92nd minute; as a substitute in a 4–1 home victory over Wigan Athletic.