McBreen made his debut for the Mariners in 1–0 away win over Melbourne Heart on 5 August 2010, in which he was substituted for Nik Mrdja in the 90th minute. His first goal came nearly a month later when heading in Matt Simon's cross in the 50th minute of a 2–0 home win over Melbourne Victory on 3 September. McBreen was sent off for the first time since returning to Australia with a second yellow card during the stoppage time of a 5–1 home defeat to Brisbane Roar on 28 November, and returned from suspension as a 52nd-minute substitute for Adam Kwasnik in a 1–1 draw away to Perth Glory on 12 December. With a second-placed finish in the 2010–11 A-League table the Mariners qualified for the finals series, and he started in their 4–2 aggregate defeat to Brisbane Roar in the major semi-final and their 1–0 win over Gold Coast United in the preliminary final. McBreen came on as a 72nd-minute substitute for Simon in the 2011 A-League Grand Final at Lang Park on 13 March 2011, and after a 2–2 extra time draw he missed one of the penalty kicks as the Mariners lost the shoot-out 4–2. He made 31 appearances and scored 5 goals for the Mariners in 2010–11.