Britain’s Emma Radocano says she needs a “tremendous effort” to beat Colombia’s Camila Osorio to reach the quarter-finals of the Washington Open.
Raducano, who will begin her title defense at the US Open this month, won 7-6 (7-5), 7-6 (7-4) in two hours and 50 minutes.
“It gives you a lot of confidence to play a match like this,” the British number one said.
Citizen Dan Evans stepped in with the retirement of American Taylor Fritz.
In hot and humid conditions, Raducanu and Osorio demand a medical reprieve.
“For me it was a pretty massive effort to really get through that,” said Radocano.
“There were many moments in both sets where you want to go for the easy option to try to finish the point early, but I’m really happy and proud of how you disciplined me when it really mattered.”
Raducano will play Russia’s Lyudmila Samsonova in the quarter-finals.
Evans, who saved match point but was 3-6 7-6 (8-6) 4-1 when Fritz withdrew, faces Yoshihito Nishioka of Japan in the quarter-finals.
Fritz said he was “embarrassed” not being able to finish the match but that he had been wearing protective boots since Wimbledon last month with a foot injury.
“I always felt like I was about to faint, and my vision was blurry,” He said on social media.
“The only thing that could really prepare me to play in these conditions… is to play in these conditions, something I was not able to do while taking care of my feet.
“Now that my feet have improved, I can finally start working on the field and be ready for the rest of the year. Sorry if I’m worried about anyone.”