Serena Williams has earned her place at the WTA Championships after reaching the second week at Wimbledon.
The world number one, who has already won the Australian Open and French Open in 2015, secured her spot at the end-of-season finals with a three-set triumph over Great Britain's Heather Watson on Friday.
In a WTA statement, the 33-year-old said: "I'm really thrilled to be the first player to qualify for the WTA Finals and I can't wait to return to Singapore to defend my title.
"Last year was my first year visiting Singapore and I really enjoyed myself. The crowd is amazing and I'm excited to be going back."
The 20-time major winner plays sister Venus Williams in the fourth round on Monday.
