The 25-year-old joined Belgium club from the Dutch Eredivisie side Heracles Almelo this summer. But the Nigerian striker as he continues to underline his importance to the team since the commencement of pre-season.
Olivier Deschacht put the home team ahead four minutes before the break at Regenboogstadion.
Onuachu, who replaced Mats Daelhi in the 56th minute equalised for Genk in the 73rd minute.
Dessers scored the match-winning goal with a well-taken effort from the penalty spot ten minutes from time.
Belgium-born has taken to social media to share his feelings after helping his new club kick off the season with a victory.
— Cyriel Dessers (@CyrielDessers) August 9, 2020
Dessers will hope to build on his impressive debut showing when Genk take on his former club OH Leuven in their next league game on August 15.