The American appeared at her first Wimbledon in 1997, the year the Latvian was born, and won it for the first time when Ostapenko was three.
For 20-year-old Ostapenko, the newly crowned French Open champion, it will be a first outing on the most famous grass court in the world.
Williams, at 37 the oldest woman in the draw with five Wimbledon singles titles to her name, has probably lost count of her appearances on the court.
She said after trouncing Ana Konjuh 6-3 6-2 on Monday she was happy for the success of her young opponent in Paris.
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"I know she had an amazing moment there. She's riding on that momentum. Confidence I'm sure. It's just been such an amazing result for her."
Ostapenko, though, can hardly remember ever watching Williams play, saying she had been keener on Venus's sister Serena when she was growing up.
"I think I was watching more her sister's matches because she was my idol," Ostapenko said after dispatching fourth seed Elina Svitolina 6-3 7-6(6).
Through her first four rounds here, the powerful young Latvian has appeared thoroughly relaxed and nerve-free.
She will need to carry that feeling into the quarter-final against her supremely experienced opponent, whose movement round the court belies her age.
"I just keep stretching. I have no secrets. I'm just doing what I always have done," Williams said.
"I think I stretch a little harder now. But only because I enjoy it."
(Reporting by Clare Lovell, editing by Pritha Sarkar)
