On a hot and humid afternoon, the US Open champion completed the win in two hours and 50 minutes - the longest straight-sets main-draw match on the WTA Tour this year - just before thunderstorms lashed down to suspend play.

Both players required medical timeouts to manage blisters during the error-strewn contest, which saw a number of breaks and swings in momentum. The British number one was a break up early on in both sets but was constantly pegged back. However, the world number 10 finally sealed her quarter-final spot against 60th-ranked Liudmila Samsonova in Washington.

"For me it was a pretty monumental effort to really get through that," Raducanu said on Thursday.

"There were many moments in both sets where you want to go for the easy option of trying to finish the point early, but, yeah, I'm just really pleased and proud of how I dug in when it really mattered.

"It was three hours on the court, and I actually warmed up for like an hour this morning. It just gives you a lot of confidence coming through a match like that."

Raducanu has struggled with her form and performances following her first Grand Slam title at Flushing Meadows last year and appointed Russian coach Dmitry Tursunov on a 'trial basis' just before Washington. She will be looking to go deep in this tournament ahead of the upcoming WTA 1000 events in Toronto and Cincinnati, as well as the US Open which is right around the corner.