The career of second-seeded Citi Open Emma Raducanu ended with a quarter-final loss to Liudmila Samsonova in Washington.
Despite the tight opening set, Radokano eventually overcame the 7-6 (8-6) 6-1 in 60th place in the Russian world.
Samsonova saved four set points en route to winning the first set before taking off in the second half with nine aces and 33 match winners.
Raducanu proved to be her worst enemy as she struggled to match Samsanova’s strength, amassing just eight winners and an ace to match 24 unintentional fouls.
At the ATP event, Britain’s second jersey Dan Evans fell in three sets to Japan’s Yoshihito Nishioka in the quarter-finals.
After losing the first set in a tiebreak, Evans raced to grab the second set convincingly.
However, he was unable to sustain that momentum in third place as the world No. 96 took a 7-6 (7-5) 4-6 7-5 victory.
Nouri will face Medvedev in the final in Mexico
Defending champion Cameron Norrie set up a showdown with world number one Daniil Medvedev in the Abierto de Tenes Miffel final with a victory over Felix Auger-Aliassime.
The British No. 1 jersey holder won 6-4, 3-6, 6-3 against the second seeded Canadian in two hours and 19 minutes in the second semi-final in Los Cabos, Mexico.
Nouri’s success, his first against Auger-Aliassime in five encounters, saw the third seed win the ATP Tour title for the third time this year.
He will now face Medvedev, who beat fourth seed Miomir Kekmanovic 7-6 6-1 to secure the number one ranking until at least the end of the US Open next month.
“You still want to defend the title, but it’s complicated,” Nouri told reporters. The start was difficult but I played very well after losing the second set.
“I try to play my best and it’s great to be back in the final. I love playing in Mexico.