Moon made his Jeonbuk Hyundai Motors debut in the opening game of the season against Daegu in the 75th minutes substitute, in a 1–0 win.[75] He scored his first goal in a follow–up match, in a 4–0 win against Suwon Samsung Bluewings.[76] Four days later, on 13 March 2019, Moon made his AFC Champions League debut, where he played 30 minutes, in a 1–0 against Buriram United.[77] At the start of the 2019 season, Moon found himself placed on the substitute bench, due to his struggling form..[78] His second goal for the club came on 6 April 2019, in a 2–0 win against his former club, Incheon United.[79] A month later on 29 May 2019, Moon scored twice for the club, in a 3–2 win against Gangwon.[80] After the match, he was named MVP Round Fourteen of the 2019 season.[81] This was followed up by scoring against Sangju Sangmu on 2 June 2019.[82] Seventeen days later on 19 June 2019, Moon scored his first AFC Champions League goal, in a 1–1 draw against Shanghai SIPG in the first leg of the AFC Champions League Round of 16.[83] Following the match, his goal was named both Goal and Top Player of the AFC Champions League Round of 16.[84] However, in the second leg, he was sent–off in the last minutes of extra time for a unprofessional foul; the match went to penalty shootout and Jeonbuk Hyundai Motors lost 5–4.[85] After the match, Moon apologised for his actions and said he should have been patient.[86] Then on 10 July 2019, Moon scored his first hat–trick of his career, in a 4–1 win against Daegu.[87] For the next two months, Moon later contributed for the club’s matches by assisting several goals, which helped the side go on winning runs in aiming to be a title contenders.[88] In a match against Suwon Samsung Bluewings on 26 September 2019, he came on as a late substitute in the 81st minute and scored the late goal, in a 2–0 win.[89] A month later on 20 October 2019 against Pohang Steelers, Moon scored his eleventh goal of the season, as well as, setting up the opening goal of the game, in a 3–0 win.[90] His goal against Pohang Steelers and performance earned October’s Goal of the Month and October’s Player of the Month respectively.[91] After missing one match, Moon returned to the starting line-up against Gangwon on the last game of the season and played 85 minutes, as Jeonbuk Hyundai Motors won 1–0 to win the league for the third time consecutively.[92] Moon finished his first season at Jeonbuk Hyundai Motors, making thirty–seven appearances and scoring eleven times in all competitions.