The 27-year-old wildcard overpowered his South African opponent with a barrage of winners to take his record to 12-2 for the season, having only won three Tour-level matches prior to this year.
“I am super happy. It was a tight match. I was really nervous,” world No. 42 Karatsev said on court.
“You never know when [success] is coming. I did a good job with my team, with my coach and it has happened now.”
He announced himself on the big stage when he enjoyed a fairytale run to the Australian Open semifinals earlier this year, losing to eventual champion Novak Djokovic.