Former world number one Maria Sharapova won her second Pan Pacific Open title after Jelena Jankovic retired with a wrist injury in Saturday's final.
It was Sharapova's first title since shoulder surgery last October and the 20th of her career. Her last tournament win came at Amelia Island in April 2008.
The Russian was leading 5-2 when seventh seed Jankovic complained of shooting pains down her right arm and called for the trainer to tape up her wrist at the changeover.
The Serb managed just two more points after a medical timeout before throwing in the towel.
“These things happen but I'll certainly take it,” Sharapova said after the abbreviated final, her second of the year after a runner-up finish in Toronto in August.
“It's great to have that adrenaline again,” added the three-times grand slam winner, set to break into the world's top 20 after coming into the Tokyo event ranked 25th.
Four of her 20 WTA Tour titles, including her breakthrough victory at the 2003 Japan Open, have come in Tokyo.