Bulgaria's Grigor Dimitrov edged second seed Andy Murray in a semi-final clash at the Acapulco International that finished in the early hours of Saturday morning to set up a title showdown against South Africa's Kevin Anderson.
Wimbledon champion Murray won the opening set but the 22-year-old Dimitrov fought back to take the next two sets on tie-breaks to win 4-6 7-6 (7-5) 7-6 (7-3) with the clock ticking past 2:30 a.m. local time.
The number four seed had never won a set in their three previous meetings and needed close to three hours to beat the 26-year-old Briton, who was trying to reach his first final since undergoing back surgery in September.
Murray, who suffered an early loss of serve in the final set, broke back with his opponent serving for the match at 5-4 but Dimitrov took control of the tie-break to close out the win.
World number 21 Anderson, who lost to Marin Cilic in the Delray Beach Open title match last Sunday, reached his second final in as many weeks with a hard-fought 6-1 5-7 6-4 win against Ukraine's Alexandr Dolgopolov in the other semi-final.
Dolgopolov, ranked 38th in the world, was also bidding for his second consecutive final after he lost to Rafa Nadal in the Rio de Janeiro Open final last week.