Sertic began his career playing for AS Egly Football in Essonne. He later had a stint at both his hometown club CSF Brétigny and ES Viry-Chatillon before going to the famous Clairefontaine academy to receive further training. Following a two year stint there, he moved to FC Girondins de Bordeaux. He gained recognition and notice from manager Laurent Blanc during the 2007–08 CFA season, in which he played in 20 matches and scored 7 goals helping Bordeaux's reserve side finish 1st in their group. He also was apart of the Bordeaux youth squad that finished runner-ups at the 2008 edition of the Coupe Gambardella losing 0–3 to a stout Rennes side.

For his efforts, he was given the opportunity to play and train with the first-team squad for the 2008–09 season. He was also included on Bordeaux's UEFA Champions League roster for their 2008–09 European campaign, though he didn't make an appearance. The midfielder finally made his professional debut on 11 November 2008 in a Coupe de la Ligue match against Guingamp appearing as a substitute playing 12 minutes. The match ended in a 4–2 victory. He made his first league appearance and start on 25 April 2009 in a 3–2 win over Rennes. Sertić played 69 minutes before being substituted out. He started again the following week against Sochaux and scored his first career goal in the 7^th minute.