Australian Nick Kyrgios has told a group of opposing fans to "man up" after swearing at them in his win over Israeli Dudi Sela in Acapulco.
Kyrgios, 21, reacted after apparently being disturbed as he prepared to serve in Tuesday's 3-6 6-3 6-3 win.
The world number 17 later laughed off Australian broadcaster 7 News' report that four fans want an apology.
Sela confronted Kyrgios after the match at the Abierto Mexicano Telcel, with the umpire coming between the players.
The incident is the latest in a string of controversies for Kyrgios who accused an umpire of being biased in his semi-final defeat by Jo-Wilfried Tsonga in Marseille last week.
He was banned for eight weeks and fined for his on-court behaviour at October's Shanghai Masters, although he accepted a 'care plan' agreement that would reduce the suspension to three weeks.
Kyrgios will play former world number one Novak Djokovic in the last eight from 04:00 GMT on Friday morning.