Defending US Open champion Emma Raducanu is finding her feet on American soil again. She advanced to the Citi Open quarterfinals Thursday with a tough 7-6(5), 7-6(4) win against Camila Osorio in 2 hours and 50 minutes, the longest straight-sets WTA main-draw match of 2022.

Here are three takeaways from Raducanu's victory:

Never count out Osorio ... but Raducanu was ready: Osorio's rise up the rankings last year was defined by a series of improbable comeback wins, and her fighting spirit from behind was in evidence against Raducanu. In both sets, the Colombian dragged herself into contention despite facing sizeable deficits.

Raducanu had a point to lead 5-1 in the first set, and three break points to go up a 5-2 double-break in the second. But Osorio deployed the full range of her variety to come within a whisker of stealing both, holding two set points at 5-4 in set one and coming two points from levelling the match at 6-5 in set two.

Less sure when ahead, Osorio aided Raducanu with double faults on both of her set points in the first set. But in both tiebreaks, it was Raducanu who shrugged off the loss of her leads to rise to the occasion. From 5-3 down in the first-set tiebreak, the 19-year-old reeled off her best trio of points -- a pass, a drop shot and a return winner -- to regain control. In the second, remarkable defence at 5-4 elicited the error from Osorio and brought up a match point for Raducanu, who converted it with a service winner.

Winning ugly could be a confidence boost: Conditions in Washington were gruelling, with temperatures hovering around 90 degrees with 62% humidity. Both players required medical timeouts for blisters. Consequently, the stat sheet wasn't the prettiest. Raducanu committed 51 unforced errors and Osorio 60.

"Honestly three hours in that condition, I think that I probably played in Landisville, Pennsylvania, last year, and I'd say there it was probably worse conditions, but I wasn't out there for three hours with the length of rallies that I was out there today," Raducanu said. "So conditions-wise it was probably hotter and tougher over there, but match-wise I think it's got to be one of the most physical matches I have ever played."

It was a contrast to Raducanu's US Open run last year, when her entire game clicked over 10 matches in three weeks. As the teenager has adjusted to the main tour this year, though, she's come out on the wrong end of a few heartbreaking losses from in front, most notably to Petra Martic and Katerina Siniakova in Indian Wells and Miami respectively.

This match could easily have turned into something similar after Raducanu failed to serve out the win at 5-4 in the second set, throwing in consecutive double faults and a tame forehand into the net. But steeling herself to rebound for the tiebreak was another step along her learning curve.

Liudmila Samsonova will be a formidable quarterfinal test: Raducanu's opponent in the last eight will be Liudmila Samsonova, who overcame Ajla Tomljanovic 4-6, 6-3, 6-2 in 2 hours and 14 minutes. They have never faced each other before.

Highlights: Samsonova d. Tomljanovic | Wang Xiyu d. Vekic

Raducanu's run this week has put her into her third quarterfinal since winning the US Open, following Cluj-Napoca last October and Stuttgart in April. Making it past that stage would be a significant barrier to pass.