Keothavong lost to Dementieva at last year's US Open
World number four Elena Dementieva made light work of beating Britain's Anne Keothavong in the first round of the West Classic in California.
The Russian cruised to a 6-1 6-4 victory in her first match since her epic Wimbledon semi-final defeat by Serena Williams earlier this month.
"She played well, definitely felt like my first match in ages," wrote Keothavong on her Twitter webpage.
Maria Sharapova made a winning return, beating Ai Sugiyama 6-4 6-7 (6-8) 6-1.
The Russian is unseeded in the tournament as she continues her comeback from shoulder surgery.
Dementieva is making her debut at the Stanford event, which features five of the top 10 women's players in the world, including both Williams sisters.
The third seed claimed she has shrugged off the disappointment of losing the longest women's semi-final match in recent Wimbledon history and is now concentrating on the hard court season.
"It's not something that ticks me off," insisted the 27-year-old, who will play either Maria Kirilenko or Anna Chakvetadze in the second round.
"It was a good experience and a good match. I was just disappointed in the way I lost."
Seventh seed Agnieszka Radwanska also made a confident start in the competition, easing to a 6-0 6-1 victory over Romania's Sorana Cirstea.
Serena and Venus Williams will return for the first time since their Wimbledon final, which Serena won to seal her 11th Grand Slam singles title.
The world number two opens against China's Na Li, while Venus plays Stephanie Dubois of Canada in the first round.
Fourth seed Jelena Jankovic is in Serena's side of the draw and will begin against a qualifier.