I didn't think I could consistently serve at 180-185 km/h," Swiatek discusses her service improvement since Fissette's arrival

Iga Swiatek has advanced to the quarterfinals in Cincinnati and will face Anna Kalinskaya tomorrow.

After her round of 16 victory against Sorana Cirstea, the world No. 3 and Wimbledon champion admitted she was surprised by her progress on serve since Wim Fissette joined her team as coach.

"Honestly, I'm the kind of player who needs to see proof. If the serves go in, then I’ll be convinced. I’d say at the start of the season and when I began working with Wim, I didn’t think I could consistently serve at 180-185 km/h. I think he’s helped me reach those higher speeds.