British number two Cameron Norrie was beaten 7-5 6-4 by Dominik Koepfer in the quarter-finals of the Mexican Open.
Norrie, who is ranked 10 places higher than the German at 61, lost a close match in one hour and 48 minutes.
Koepfer needed five match points to secure victory and reach his first ATP Tour semi-final.
In the doubles, British brothers Ken and Neal Skupski beat Briton Jamie Murray and Brazil's Bruno Soares 6-3 3-6 12-10.
Koepfer will play compatriot Alexander Zverev, who received a walkover win against Casper Ruud, in the semi-finals.
Stefanos Tsitsipas beat Felix Auger-Aliassime 7-5 4-6 6-3 and will play Lorenzo Musetti, who beat Grigor Dimitrov 6-4 7-6 (7-3), in the other semi-final.
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