Mirra Andreeva says she surprised herself with her nerveless performance after beating Jessica Pegula to become the youngest player for 22 years to reach the WTA Finals showpiece.
French Open champion Andreeva came back from a break down in both sets to win 6-3 6-4 in Indian Wells, California.
The 19-year-old Russian is the youngest finalist at the season-ending event since Maria Sharapova, who was 17 when she won the title in 2004.
Victory over American Pegula ensures Andreeva will finish the year as world number two.
"I did not feel one bit of pressure today, I don't know why," Andreeva told Sky Sports.
"Usually I feel like on these important points or when I have to close out the match or the set I get so tight.
"But for some reason today I was just playing. I was just not thinking about anything, just trying to enjoy."
Tournament debutant Andreeva has yet to drop a set and has not lost more than four games in any of her eight sets.
The 18 games she has lost is the fewest for a finalist at the WTA Finals since the round-robin format was introduced in 2003.
Under the guidance of coach Conchita Martinez, Andreeva has developed her serve into a real weapon.