Youth career Triantis' youth career began in 2009 at
APIA Leichhardt Tigers before moving a year later to
Sydney Olympic FC where he quickly forced his way into the First Grade squad. After amassing 49 games for Olympic and winning a title with them in the process, Peter was brought into the
Sydney FC youth setup in 2012 under Brian Dene and impressed early in a pre-season youth tournament (2012 Vietnam Youth Cup) and then went on to play in the Sydney FC
National Youth League squad.
Sydney FC Triantis made his
A-League debut for
Sydney FC on 22 December 2012 against the
Newcastle Jets, where he came on as a 30th-minute substitute for
Brett Emerton. A week later, he made his first start for the team against the league-leading
Central Coast Mariners where
Sydney FC won 1–0. After being in and out of the team, Triantis received another start on 10 February 2013 where he scored his first goal for
Sydney FC against
Brisbane Roar. The goal gave Sydney FC a 2–1 lead and turned out to be the winning goal. On 7 March 2013, Triantis signed a 2-year deal with Sydney FC and subsequently his first senior deal in professional football to take him through to the end of the 2014/15
A-League season with the club. At the start of the 2013/14 season, Triantis was ruled out for 4–5 months with
osteitis pubis allowing
Matt Thompson to sign as injury cover for the young midfielder. Triantis was released from his contract at the conclusion of the 2014–15 season. ==Honours==