In hot conditions in Washington DC, both Raducanu and Sakkari struggled to hold their serves in the opening set, with the Briton converting three of her six break points and her opponent two from four.
However, at 4-4, Raducanu struck the decisive blow, breaking Sakkari’s serve for the third time before converting a second set point.
The 29-year-old Sakkari, runner-up at the tournament in 2023, had an opportunity to take the match into a decider after breaking serve in the sixth game of the second set and saving two break points for a 5-2 lead.
However, Raducanu roared back to win five consecutive games, including converting two of her five break points, to take the second set 7-5.
She received attention from a physio during the second set and later said she felt a “bit wobbly” due to the heat.
“It was brutal today,” added Raducanu. “It was a long match, the first set was over an hour. You just have to enjoy suffering and leave it all out there on the court.
“Maria played an incredible match and the conditions really suit her with the liveliness of her game.
“I need to prepare [for the doubles] and get out of the heat. I felt a bit wobbly at the back end of the second set.”
In the men’s doubles, Britain’s Neal Skupski and Australian partner John-Patrick Smith reached the semi-finals after coming back from a set down to upset fourth seeds Michael Venus and Yuki Bhambri 3-6 6-4 10-7.