The opening semifinal match featured an all-American duel between Learner Tien, who finished second in the Blue Group, and close friend Alex Michelsen at King Abdullah Sports City.
It would take Tien five sets to overcome the second seed with a 2-4, 4-2, 1-4, 4-0, 4-1 solid win after one hour and 36 minutes to become the third American player to reach the Next Gen ATP Finals championship match.
Making his second appearance at the season-ending event, Michelsen advanced to the semifinals undefeated.
Meanwhile, Tien, 19, reached the semifinals by clinching a 4-2, 4-2, 3-4(4), 4-3(5) hard-fought victory over top seed Arthur Fils on Friday, the highest-ranked triumph of his young career.
Their first meeting at tour level saw the Californian natives leaving nothing on the table with a ticket to the final at stake on Saturday in Jeddah, Saudi Arabia.
Michelsen, who came out on top of the Red Group, hit first, notching the opener 4-2.
However, his fellow compatriot showcased some ferocious ball-striking skills to set level at one set apiece.
The second seed quickly reacted, controlling the third set to take a 2-1 lead.
Nonetheless, the Winston-Salem quarterfinalist, who qualified for the world’s best 20 and under singles players of the season tournament for the first time, not only navigated out of danger but took control of the match, playing aggressively from the baseline, pocketing the remaining two sets.
Courtside, the fifth seed, commented: “I can’t put it into words right now. I am really happy with the win, but I hate it was against him. But that is just how it goes.
“I started smiling when I came out here and saw him on the other side of the net, but I am really happy to get through and think I played really well.”
2024 has been a standout season for the American player, who set off the year ranked at world No. 453 and now finds himself at No. 122 in contention to win the biggest title of his career when he faces unbeaten Joao Fonseca on Sunday.
Speaking about the upcoming title match, Tien said: “It would be amazing to win. I have one more to go, so I hope I can get it done.”
For his part, the Brazilian teenager finished the Blue Group stage 3-0, becoming the force to beat.
The first player from Brazil to contest the year-end venue defeated Frenchman Lucas van Assche 4-2, 4-2, 4-1 in 60 minutes, progressing to the showdown without facing a break point all match.
“Today was a great match. I played really solidly,” Fonseca outlined in his on-court interview. “I did what I talked about with my coach. He didn’t have too many chances because I was playing aggressively and making all the shots.”
Throughout the event, the 18-year-old has raised eyebrows with his explosive tennis display, great depth of shot, and superb court coverage.
Across his group-stage campaign, the eighth seed beat Tien in four sets.
Against Czeck Jakub Mensik, he was made to work, earning a monumental 3-4(4), 4-3(8), 4-3(5), 3-4(4), 4-3(5) victory on Friday.
Next, the two youngest players left on the field will face one another again in Jeddah, a battle for the title and glory.
“I’m playing at a very high level. I am just very proud of myself and the way I’ve been with my routine this week, so focused,” Fonseca added.
“With my family here and my three coaches, it’s really nice.”