Heather Watson was knocked out of the Seoul Open at the first hurdle as she lost 6-3 0-6 6-1 to Sara Sorribes Tormo.
Briton Watson, who had moved back into the top 100 after reaching the third round at Wimbledon, has now failed to get past the first round in Korea in four attempts.
Sorribes Tormo, ranked 14 places lower than Watson, broke serve four times in the final set to advance after one hour and 36 minutes.
The Spaniard will now take on third seed Kristyna Pliskova or local wildcard Han Na-lae in the next round.
Heather Watson lost in three sets to see her Wimbledon hopes ended by Victoria Azarenka.Read the full story ›
Heather Watson matches her best run at Wimbledon with an excellent victory over 18th seed Anastasija Sevastova.Read the full story ›
Heather Watson became Britain's latest Wimbledon finalist alongside Finn Henri Kontinen in the mixed doubles.
The pair, who had never played a match together prior to this tournament, defeated Oliver Marach of Austria and Latvia's Jelena Ostapenko 7-6 (7/1) 6-3 in the semi-finals on Court One.
Watson will now hope to make it a British double when she and Kontinen follow Andy Murray onto Centre Court on Sunday to take on Colombia's Robert Farah and Anna-Lena Groenefeld of Germany.
Great Britain's Heather Watson has lost 3-6 6-0 12-10 to Germany's Annika Beck in the first round at Wimbledon.
Heather Watson beat Yanina Wickmayer to progress to the fourth round of the Miami Open.Read the full story ›
British number one Heather Watson has been knocked out of Wimbledon by Serena Williams, despite a battling performance which almost saw the underdog take a thrilling final set.
Watson lost 6-2, 4-6, 7-5 after a remarkable comeback and led in the final set 3-0 before being pegged back. Speaking following the game, Williams - the tournament's top seed - praised her opponent and said Watson "should have won".
"She really gave her all and showed how good she is," she told BBC Sport.
British number one Heather Watson has taken Serena Williams in the third set of their third-round clash at Wimbledon this evening.
Watson, making only her second-ever appearance in Round 3, broke Williams' serve twice, to win the set 6-4, after losing the first by six games to two.
Heather Watson's preparation for the Australian Open remained on track as she beat Sloane Stephens to reach the quarter-finals of the Hobart International.
The 22-year-old world number 49 needed a little over an hour to dispatch American Stephens 6-3 6-1 and the Briton will next play Roberta Vinci. The Italian two-time US Open quarter-finalist fought back to beat Annika Beck of Germany 3-6 6-3 6-3.
British number two Heather Watson has said that recent illness held her back after she was knocked out of Wimbledon by American Madison Keys.
Watson, who suffered from glandular fever earlier this year, said:
I feel like my game isn't back yet.
I don't think I served well today. I didn't have a high first-serve percentage.
My reactions are slow. I'm not moving like I usually move, getting balls back.
I don't feel like my game's there yet, so that will come back with time.
I knew going in it was going to be a tough one - and it was.