 On his official debut for the club on 17 September, he scored his first professional goal to confirm a 4 – 1 win against Olympiacos at the Karaiskakis Stadium in the group stage of the 2013 – 14 UEFA Champions League. Five days later, Marquinhos made his Ligue 1 debut as a starter in a 1 – 1 draw against AS Monaco. His first league goal for the club came on 28 September, the first in a 2 – 0 win over Toulouse. On 2 October he scored the second goal in a 3 – 0 Champions League group victory against Benfica. Marquinhos, who was playing due to injury to Thiago Silva, expressed surprise at his goalscoring form at the start of his PSG career.
