At the start of the 2017 season, Reginiussen came on as 88th minutes substitute against SK Brann in the first ever the inaugural Mesterfinalen and scored a goal in the stoppage to help them win 2–0 win. He continued to help the club to a winning start, as well as, keeping four clean sheets in the first five league matches of the season. He then scored his second goal of the season, in a 9–1 win against Tynset in the second round of the Norwegian Cup on 24 May 2017. Two months later on 12 July 2017, Reginiussen scored his third goal of the season, in a 1–1 draw against Dundalk in the first leg of the UEFA Champions League Second Round. He helped the side beat 2–1 after the game went extra time, winning 3–2 on aggregate to go through to the next round. Since the start of the 2017 season, Reginiussen continued to be in the first team regular, playing in the centre–back position, and formed a partnership with Skjelvik and Björdal; earning praises from the Norwegian media for his performance. Later in the 2017 season, Reginiussen appeared as an unused substitute against Aalesunds on 4 November 2017, as the club lost 2–1, but nevertheless become Champions for the third time in a row. Following this, he won the league’s Player of the Year. It was announced on 23 December 2017 that Reginiussen signed a contract, keeping him until 2019. Despite being sidelined on three occasions during the 2017 season, Reginiussen went on to make thirty–six appearances and scoring three times in all competitions.