The 24-year-old compatriot Geoffrey Cave with two solid right hands at the bout held at Manchester Arena.
“Sorry to everyone that missed me fighting,” Okolie tweeted.
“The good news is a Won by KO in 20 seconds!! Bad news is I’m back in the cage for now.”
London-based Cave, 33, has now lost all three of his professional fights.
Okolie competed at heavyweight and lost to Cuban Erislandy Savon at the last-16 stage at the Rio Olympics.
He had boxed Savon once before and lost via a first-round stoppage, but at the second attempt he went the three-round distance with the Cuban who would eventually claim a bronze medal.
Savon had lost to Nigerian born Anthony Joshua at the London 2012 which also inspired Okolie.
Okolie had explained that the likes of Joshua lured him into boxing.
“Before I started boxing properly I was working in McDonald’s, and I was watching the Olympics during my breaks whenever I could,” he told Sky Sports News HQ.
“It was the only thing to do! There was a particular break where Usain Bolt won the 100m then Anthony Joshua won gold. I felt something then.
“It was really inspirational. I started putting more work into training, and believing it more.”
Okolie is scheduled to fight on the undercard of Ricky Burns’ super-lightweight unification bout with Julius Indongo on April 15.