In parallel with his performances at the youth academy that year, he played in the Super League of Dnipropetrovsk region (8 matches, 2 goals). On the eve of the start of the 2017/18 season, he was transferred to the first team of the "Dnipro" club. Debuted on the "Dnipro" T-shirt on July 15, 2017 in the lost (1: 2) away match of the 1st round of Group "B" of the Second League against Odessa's "Real Farma". Oleg came on the field in the starting lineup and played the whole match, and in the 57th minute received a yellow card. He scored his debut goal in the T-shirt of the "Dnipro" club on August 5, 2014 in the 53rd minute of the victorious (2: 1) home match of the 4th round of Group "B" of the Second League against Petrovo's "Ingulets-2". Ilin came on the field in the starting lineup and played the whole match. In the first part of the 2017/18 season he played 22 matches in the Second League, in which he scored 2 goals.
During the winter break of the 2017/18 season, the Ukrainian media reported on the possible departure of Oleh Ilin from "Dnipro", after which the young player went to watch "Kolos". At the end of February 2018, he signed a contract with the Kovalivka's club. He made his debut for "Kolos" on March 18, 2018 in the victorious (4: 2) away match of the 23rd round of the First League against "Obolon-Brovar" from Kyiv. Oleh came on the field in the starting lineup, in the 70th minute scored a goal in the gate of Kyiv, and in the 90th minute was replaced by Yevhenii Morozko. He played one and a half seasons in the First League as a member of Kovalivka, helped the team win a ticket to the Premier League. He made his debut in the Premier League on July 30, 2019 in a victorious (2: 1) home match of the 1st round against "Mariupol". Ilin came out in the starting lineup and played the whole match, and in the 69th minute received a yellow card.