Kostyuk was one of the leading players in the clay-court swing, claiming two successive titles before reaching the French Open semi-finals.
The 24-year-old did not play a tournament before Wimbledon, instead returning home to Ukraine and having a holiday in Greece.
While she said she was optimistic of transferring her clay form to the grass, she had also not won on the surface for two years going into this year’s championships.
“I feel like a lot of years that I played here, I played horrendous,” Kostyuk said.
“I could not find my tennis on this surface, on any tournament. It was a really complicated relationship for me.”
Kostyuk still was not convinced when she arrived in London almost three weeks ago.
Losing practice sets to 44-year-old Serena Williams and Jessica Pegula did not swell her confidence, but the words of coach Sandra Zaniewska did.
“I turned to Sandra and said: ‘Can you please tell me, honestly, right now, if you think that grass suits my game?’ She said: ‘100%’,” Kostyuk said.
“That gave me something to hold onto.”