Eileen King defeated opponents 70 and 60 years younger than her in The Green LTA Ratings tournament in St Leonards.
The 80-year-old belied her age as she defeated Rebecca Godfrey, ten, from Pevensey, 6-4, 6-0 before overcoming Carol Freer, 20, 7-6, 6-3. to reach the knockout stages.
Eileen almost made it a hat-trick when she held three match points against Madison Walters before losing 6-2, 2-6, 7-6.
Her son Richard, who refereed the nine-day event based on tennis' equivalent of the golf handicap system, said: "My mother enjoyed herself. What was remarkable was that when she beat Carol it was a very hot day. Yet after the first set, which took an hour, she was so cool while Carol was sweating.
"She lost in the end because, at her age, she is not the fastest mover. Maybe she let the match points slip away because of LACK of experience!
"In truth, although she has played a few tournaments elsewhere, she has been a regular at The Green tournament since 1984."
The women's final, between Elisa Mansell (Seaford),12, and Justine Gedge (St Leonards), 16, was postponed due to illness until next week.
King said: "Elisa had a very heavy cold. Really we should have given the title to Justine but the event isn't quite as serious as Wimbledon. The important thing is for the girls to play a bit more tennis. Justine was happy to go along with the decision."
Michael Wenham (Ditchling), 13, won the men's event, He beat Pierre-Emile Rollux 6-2, 6-4 in the final.
Wenham triumphed against Kevin Gissing (Portsmouth) 6-3, 6-4 in the semi-finals, while Rollux defeated David Butler (Eastbourne) 5-7, 6-4, 7-6.
King said: "David is in his early fifties and did fine, but it was good to see the kids doing so well."
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