Coco Gauff has become the youngest player since Maria Sharapova in 2005 to qualify for the WTA Finals in singles.

Gauff and Pegula will be the first Americans to play at the WTA Finals in singles and doubles since Serena and Venus Williams in 2009.

Gauff sealed her place by reaching the third round of the Guadalajara Open.

The WTA Finals take place in Fort Worth, Texas, from 31 October-7 November.

"It means a lot," said world number seven Gauff, who beat Elisabetta Cocciaretto 7-6 (7-1) 6-3.

"Honestly I didn't think about it until I realised how close I was and I think I went maybe a little bit nervous in the end but I'm super excited to be playing in the WTA Finals, especially in the USA, and qualifying in singles and doubles is definitely a good achievement.

"I didn't expect that when I set my goals at the beginning of the year. I'm really happy and I hope I can do a good performance there."

Gauff will be the youngest American to play at the WTA Finals since Lindsay Davenport 28 years ago.

She reached her first Grand Slam final this season, losing to Poland's world number one Iga Swiatek at the French Open, while she also made the quarter-finals of the US Open for the first time.

Gauff joins Swiatek, Pegula, Ons Jabeur and Caroline Garcia in qualifying for the eight-woman singles field, with three places still to be secured.