The British star reached the quarter-finals in Stuttgart, where she was beaten by the all-conquering Iga Swiatek, and she won her opening match in Madrid against Tereza Martincova as she gets used to life without a coach again.
It was a slightly uncomfortable opening set for Raducanu but she then breezed through the second to win 7-6 6-0.
Next up is a familiar foe in Ukraine’s Kostyuk, who is also 19.
The pair met a number of time as juniors before their first professional meeting at the end of last year at the Transylvania Open. Kostyuk cruised to victory that day, winning 6-2 6-1 in the quarter-finals, and Raducanu will be looking for a much better display.
“All throughout juniors she was always the favourite when we played,” Raducanu said ahead of Saturday’s match.
“She was considered much better. Yeah, it’s a funny one. When we played last year she played very good, but also I wasn’t very well that day. So it’ll be an interesting match-up.”
Date, venue and UK start time
The round of 32 match between Emma Raducanu and Marta Kostyuk will take place on Sunday, May 1.
The action is scheduled to get underway at approximately 3.15pm GMT.
Garbine Muguruza or Anhelina Kalinina await the winner in the next round.
How to watch Emma Raducanu vs Marta Kostyuk
TV channel: The match will be broadcast on the Amazon Prime streaming service.
Live stream: Amazon Prime subscribers will be able to watch the match either on their website or through the app.
Emma Raducanu vs Marta Kostyuk head-to-head record
The pair have met once before on the WTA Tour, when Raducanu managed just three games last October in Romania.
Raducanu wins: 0
Kostuyk wins: 1