The former Denmark-based striker scored the winning goal for Portland Timbers 11 minutes from time to hand them all three points on the opening day of the season.
Columbus Crew were looking to gain revenge for their defeat to Timbers in the final MLS Cup last season, but Adi's strike prevented that.
Diego Valeri gave Timbers the lead in the first half, with Federico Higuain grabbing the equaliser for the visitors in the 68th minute. Last season, Adi scored 19 goals to guide Timbers to their first title since joining the league in 2011. He is in line to make his debut for Nigeria in this month's 2017 Africa Cup of Nations qualifiers against Egypt.