World number two Novak Djokovic was knocked out of the Mexico Open quarter-finals in straight sets by Australian Nick Kyrgios.
The Serbian top seed lost 7-6 (11-9) 7-5 in one hour, 47 minutes in what was the first ever meeting between the two.
Djokovic, 29, was back in action in Acapulco this week for the first time since his second-round exit at the Australian Open in January.
Kyrgios, 21, faces American Sam Querrey in Friday's semi-finals.
Spain's Rafael Nadal and Croatia's Marin Cilic meet in the other semi-final.
In the women's event, there were wins on Thursday for Ukraine's Lesia Tsurenko and Croatia's Mirjana Lucic-Baroni.