Cameron Norrie saw his tilt at the Truist Atlanta Open title ended at the quarter-final stage by Finland’s Emil Ruusuvuori 7-6 (1) 6-3.
The third seed, who defeated Nick Kyrgios in the previous round, held serve but failed to make inroads into his opponent’s in the first set as it went to a tie-break.
But Norrie lost the first six points – three on his serve – and Ruusuvuori’s fourth break sealed a 1-0 advantage.
Breaks at 1-0 and 3-2 against the British No 2 were the difference in the second set, as world No 78 Ruusuvuori served out for the win.
He will go on to meet Brandon Nakashima in the semis after the American saw off Jordan Thompson 7-6 (5) 7-5, while also through to the last four is Taylor Fritz who toiled for nearly three hours to beat Reilly Opelka 7-6 (5) 6-7 (3) 7-6 (4).
John Isner prevailed in his rain-delayed match, seeing off Australian Christopher O’Connell 7-6 (5) 6-7 (3) 6-4.
Elsewhere, top seed Casper Ruud is one match away from becoming the first player since Andy Murray a decade ago to win three ATP titles in as many weeks after reaching the final of the Generali Open in Kitzbuhel.
The Norwegian is bidding to secure his fourth singles trophy of the year after registering an 11th successive victory by beating Arthur Rinderknech in a rain-interrupted 6-3 7-6 (7) victory.
Pedro Martinez stands in his way after the Spaniard rallied from a set down to defeat Daniel Altmaier 4-6 6-3 6-3 to secure his first ATP Tour final.
Murray was the last player to win three weeks in a row in October 2011 after victories in Bangkok, Tokyo and Shanghai.