Into the January transfer window, fan favourite Matthew Jurman joined K-League club Suwon Samsung Bluewings, while keeper Vedran Janjetović swapped with Andrew Redmayne to cross city rivals, Western Sydney Wanderers after a dispute about not playing after being displaced by Vukovic. To replace Jurman, Dutch defender Jordy Buijs signed. The team was able to go on undefeated for 19 games in the league before eventually being defeated 1–0 in a controversial game against the Wanderers. This defeat only made the team stronger, as they went the remainder of the season undefeated, gaining 19 points out of a possible 21 for the remaining 7 games. His team was eventually crowned premiers after Melbourne Victory was unable to defeat Brisbane Roar, while Sydney had 4 games remaining. Arnold's 3rd season with Sydney proved fruitful, in addition to winning the premiership, the squad had broken multiple records, including the most points in a single season, breaking Brisbane Roar's 2010–11 season of 65 points in 3 fewer games with 66 points, as well as being the only top-flight football team in Australia to stay outright 1st throughout the whole season. Arnold was also named Coach of the Year at the Dolan Warren Gala Night. He ended the season with a 1–1 in the Grand Final, winning 4–2 on penalties against Melbourne Victory, becoming the first manager to win the championship with more than one club. Arnold went on to win the 2017-2018 Premiership, becoming the first coach in A League history to win back to back Premierships