Japan's veteran Kimiko Date-Krumm won her opening match at the Pan Pacific Open on Monday, then virtually ruled out playing in Tokyo at the 2020 Olympics when she will be almost 50.

"Eh? I'll be 50. Fifty!" Date-Krumm told AFP with a broad smile when asked about returning to the same waterside venue to compete in the Tokyo Games.

"I'm not (Martina) Navratilova," added the former world number four, who reached the quarter-finals in Seoul last week.

"You're asking if there's a one percent chance? Well probably it's 99.9999 percent I won't, but I suppose you never say never 100 percent.

"It's almost impossible, though I'd like to be involved in some capacity and support the next generation of players coming through."

Date-Krumm's 6-2 4-1 victory over qualifier Anastasia Rodionova in the first round of the $2.3 million Pan Pacific Open, hastened after the Australian retired with an abdominal strain, gives the world number 63 a crack at another Aussie in the shape of 12th seed Samantha Stosur.

"I don't think about my age anymore," said Date-Krumm, who turns 43 this week and achieved her career-high ranking back in 1995.

"Stosur is big and powerful. I'm not crazy about that but I'll see what I can get out of my punctured body and see what happens."

Former French Open champion Ana Ivanovic, runner-up to Martina Hingis in Tokyo in 2007, flattened Germany's Annika Beck 6-1 6-1 as the Serbian pin-up, who once held the world's top ranking, swept into the last 32.

Ayumi Morita's 7-6 6-3 upset of Britain's Laura Robson, and wildcard Misaki Doi's 6-7 6-0 7-5 victory over American Varvara Lepchenko made it a good day for Japan at the 30th edition of the Tokyo tournament.

World number one Serena Williams, who won her 17th grand slam singles title at the US Open, was a late pull-out from the tournament, citing fatigue.

Two-times Pan Pacific champion Maria Sharapova withdrew due to shoulder pain.