Singapore — Madison Keys is the first American outside of Serena and Venus Williams to earn a berth at the year-end WTA Finals in more than a decade.
The last American other than a Williams to play at the season-ending tournament was Lindsay Davenport, a former coach to Keys, who last appeared in the 2005 Finals.
Keys debut in the WTA Finals, being held this coming week in Singapore, came courtesy of her winning a second career title in Birmingham, England, and reaching finals at Rome and Montreal.
She also played in the Olympic semifinals, just missing out to Petra Kvitova for the bronze medal.
"It's always been a big goal of mine to make the Finals, so being here is a huge accomplishment for me," Keys said. "I definitely want to do well here, and prove that I've worked really hard to get here and I'm here for a reason."
The 21-year-old Keys, who joined the top 10 rankings at No. 7 earlier this month, is also the first American to debut in the top 10 since Serena Williams in 1999.
"I think it was definitely really surprising that I was the first American to break into the top 10 for that long," Keys said. "There have been a lot of great American players who I thought had made it, but obviously not.
She added, "I just look at it as a great accomplishment and a huge opportunity to go out and play tennis, and have fun and maybe inspire some more young American girls to pick up some racquets."
Second-ranked Serena Williams pulled out of this year's WTA Finals for the second consecutive year having won the title in 2014, the first year the event moved to Singapore.
Williams, who hasn't played since a semifinal loss to Karolina Pliskova at the US Open, cited a persistent right shoulder injury as reason for not competing.
Keys will face Simona Halep in her first of three round-robin matches on Sunday. They are in the round-robin Red Group along with world No. 1 Angelique Kerber and Dominika Cibulkova.
The White group consists of defending champion Agnieszka Radwanska, reigning French Open champion Garbine Muguruza, US Open finalist Karolina Pliskova and either Johanna Konta or Svetlana Kuznetsova.
Konta, who would be the first Briton to play in the year-end event since Jo Durie in 1984, already is in Singapore. Kuznetsova needs to defeat Daria Gavrilova in the Moscow final on Saturday to snatch the eighth position from Konta.
Kerber overtook Williams for the No. 1 ranking after she won the US Open last month, her second career grand slam title. In January, Kerber upset Serena Williams in the Australian Open final to win her first major.
Kerber, who became the first German woman since Steffi Graf to attain the top ranking, also won the Olympic silver medal in Rio.
"As a player I change a lot," Kerber said of this season. "I have much more confidence right now. I know how to play the big tournaments also mentally, how to win really tough matches in tough situations, or like playing finals in big tournaments, big stages."
Radwanska arrived in Singapore to defend her title having won three tournaments this year - Shenzen, New Haven and Beijing.
"There is always a little bit more pressure when you really have to defend a big title, a lot of points," Radwanska said. "But on the other hand side, when you're Top 5, top 10, you pretty much defending every week more or less."