World number one Elena Rybakina hailed her "amazing achievement" after securing the year-end top ranking with a 6-2, 6-3 win over fellow Kazakh Yulia Putintseva in Japan on Thursday.
Rybakina became world number one for the first time last month in winning the US Open, replacing Aryna Sabalenka at the summit.
She ensured she will start 2027 on top after a comfortable opening match in Tokyo, swatting aside world number 67 Putintseva at the Pan Pacific Open in 70 minutes.
The achievement capped a year in which Rybakina also won the Australian Open in January and now has three Grand Slam titles.
"It means a lot, this is something we worked for with the team," said the 27-year-old.
"So many great players and we are all really close to each other, and I'm happy that now with last week and with today's win I made it possible to secure number one at the end of the year.
"It's an amazing achievement and hopefully we can continue this way next year," she added.
Moscow-born Rybakina has already secured her place at next month's season-ending WTA Finals at Indian Wells.
She arrived in Tokyo after winning her fourth title of the season last week at the Ningbo Open in China.
She sent down six aces against Putintseva and saved the only break point she faced.
"Today the serve definitely helped me in the important moments," she said.
"I was just trying to pick my spot and I think today with a closed roof and a combination of the balls and the court made me feel better serving.
"I'm glad today it worked."
Rybakina's opponent in the quarter-finals will be Canada's Leylah Fernandez, who she beat in the Ningbo final.
Rybakina said she had not had time to explore Tokyo but planned to indulge a new hobby when she gets a chance.
"Because of my coach I am a little bit following Pokemon cards now," she said.
"I'm not a huge fan but he is so I know a little bit, and we were getting some cards, opening them and trying to find some important ones."