Krajinović, who progressed to the last four after world number one Rafael Nadal withdrew prior to their quarter-final yesterday, produced a superb performance to claim a 6-4, 6-7, 7-6 win at the AccorHotels Arena.

The 25-year-old had never reached the final of an Association of Tennis Professionals (ATP) Masters event before the tournament in the French capital but stunned the big-serving American to end that record.

The victory for the world number 77 ensured Isner cannot qualify for the season-ending ATP World Tour Finals event at London's O2 Arena later this month.

Krajinović will go up against another player from the United States in Jack Sock, who beat Frenchman Julien Benneteau 7-5, 6-2 in today's other semi-final.

"The emotions are amazing," the emotional Serbian said.

"It is the best day of my life.

"But the tournament is not over yet. 

"I'll prepare for tomorrow and then we'll see.

"I think it's going to be an interesting match and I will give everything what I have to finish the year strong." 

Julia Görges of Germany and American Coco Vandeweghe will compete for the Women's Tennis Association Elite Trophy after both players won their respective semi-finals in Zhuhai today.

Görges, the seventh seed, dominated her clash with Latvian Anastasija Sevastova on her way to a comfortable 6-3, 6-3 victory.

Vandeweghe hit a total of 32 winners as she overcame Australian Ashleigh Barty by the same scoreline in the Chinese city.