Reigning US Open champion Emma Raducanu has reached her second quarter-final of the season, beating Camila Osorio in a gruelling two-set encounter at the Citi Open.

After battling it out for close to three hours, the British No.1 triumphed 7-6 (7-5) 7-6 (7-4) on a hot and humid Thursday afternoon.

Raducanu will now meet world No.60 Liudmila Samsonova for a berth in the semi-final after she beat Ajla Tomljanovic.

Samsonova had to come from behind to beat the Australian, eventually winning 4-6 6-3 6-2.

With the temperature in the 90s fahrenheit (30s celsius), the second-seeded Raducanu took a medical timeout late in the second set to get treatment from a trainer for blisters on her racket-wielding right hand.

Osorio was visited by a trainer earlier.

Raducanu's only other quarter-final appearance in a dozen tournaments in 2022 came back in April on red clay at Stuttgart, Germany, where she lost at that stage to No.1-ranked Iga Swiatek.

Raducanu, who won the US Open at Flushing Meadows as a qualifier a year ago at age 18, was made to fight all the way against the 20-year-old from Colombia.

After the players met for a hug at the net, Raducanu appeared to be too exhausted for a full wave to the crowd.

"I think I died about three times in that match and I came back - honestly, I don't know how," Raducanu said in her post-match comments.

"Camila is such a battler. I was working so hard for every single point.

"When she comes back, the dynamic of the match changes a bit, so I am just really pleased to have got through that one."