Sloane Stephens suffered an early exit at the Wuhan Open as Naomi Osaka was forced to withdraw from the tournament.
American Stephens, the ninth seed, fell at the first hurdle despite winning the opening set against Anett Kontaveit in the final match on Sunday.
The 2017 US Open champion led 4-2 at one stage in the second only to be pegged back by her Estonian opponent, who broke again in the 12th game to force a decider.
Both players lost their serve midway through the third set before Kontaveit - who won just two games when the pair met at the French Open earlier this year - broke to love to seal a 4-6 7-5 6-4 triumph.
Osaka, meanwhile, will not be present in China due to illness, the US Open champion making the decision not to travel after losing in the final of the Tokyo Open.
MIXED FORTUNES FOR SEEDS
Stephens was not the only notable name to be on the wrong end of an upset; Elise Mertens, seeded 15th, lost in straight sets against Aliaksandra Sasnovich.
However, 13th seed Daria Kasatkina overcame Lesia Tsurenko in straight sets to progress, a 6-4 7-5 result avenging a loss against the Ukrainian at Birmingham earlier in the year.
Julia Goerges, the 11th seed, was taken to three sets by Marketa Vondrousova, eventually winning 6-3 3-6 7-6 (7-4) after two hours and 40 minutes on court.
BIG NAMES RULED OUT
Tournament organisers suffered a blow with Osaka's announcement, lucky loser Polona Hercog taking her place in the main draw.
The world number seven had lost in straight sets to Karolina Pliskova in Tokyo in her first event since lifting the trophy at Flushing Meadows.
Still a good week, thanks for the support ありがとう pic.twitter.com/z7SwIBt9Gl— NaomiOsaka大坂なおみ (@Naomi_Osaka_) September 23, 2018
"I'm very sorry to have to withdraw from Wuhan. I look forward to playing in Wuhan next year," Osaka said in a statement.
Former world number one Victoria Azarenka had already pulled out because of a viral illness, while a respiratory problem has put paid to Magdalena Rybarikova's hopes of competing.
Still, a strong field includes the top five in the world, led by the top-ranked Simona Halep, who has received a bye through to the second round.
|Canelo v Fielding: Tale of the tape|
|Juventus defender Cancelo has knee surgery|
|Canelo v Fielding: Alvarez and Rocky make weight in New York|
|Spalletti does not fear another mid-season crisis at Inter|
|Salah headlines CAF Player of the Year shortlist as Koulibaly misses out|
|Beckham Jr. out of Titans clash|
|Lipsky hits the front at Leopard Creek|
|Pederson coy over Wentz back injury|
|Liverpool ´not really likely´ to be active in January window, reveals Klopp|
|Always on the move and unpredictable - Pavard reveals surprising choice over toughest opponent|
|We need to get back to respect - Lampard alarmed by hate in football|
|Giles returns to England to replace Strauss as director|
|Hansen has no issue with Milner-Skudder Toulon switch|
|Juventus to rest Ronaldo after Torino showdown|
|Titmus strikes gold again as world records tumble in Hangzhou|
|Malinga to captain Sri Lanka in New Zealand|
|Rivaldo would like ´excellent´ Isco at Barcelona|
|United a long way from Mourinho´s vision|
|´Klopp denies an answer!´ - Liverpool boss dismisses questions about ´world-class´ Pogba|
|Returning Nowitzki ´so tired´ after making NBA history|
|Aguero and De Bruyne in contention for Manchester City v Everton|
|Simeone has no plans to cash in on Costa|
|Canelo v Fielding: Alvarez´s greatest nights|
|Fabregas: Chelsea being unfairly scapegoated over racism allegations|
|Crisis? What crisis? Klopp focuses on defensive solutions for United clash|
|Hope cannot inspire Windies as Bangladesh cruise to series win|
|Benitez picks up Premier League Manager of the Month award|
|Chavez, Marquez and Canelo - Mexico´s greatest multi-weight world champions|
|Bale set to miss Real Madrid v Rayo Vallecano|
|Robben out until January as Bayern look to avoid serious injury|
|Milan avoid UEFA ban in FFP punishments.|
|Mourinho compares Liverpool to ´an amazing house´ but insists trophies matter|
|Brisbane Roar 2 Melbourne Victory 4: Muscat´s men hit A-League summit|
|Bumrah confident second Test is ´in the balance´ after India recovery|
|Isco gesture was for a corner or foul, claims Solari|
|Harris leads Australia into ascendancy on day one|
|ATP announces candidates to host future Finals|
|Ronaldo: Juventus fans refuse to lose to Torino|
|Hero Rivers feared he had cost Chargers in KC|
|Williams would welcome Llorente back to Athletic Bilbao|
|Liverpool v Manchester United: Minding the gap|
|Milan elimination unjust, fumes Leonardo|
|Paul hails ´sick´ Harden after record-breaking display|
|Liverpool v Manchester United: Salah, Mane and Firmino v Rashford, Martial and Lukaku in Opta number|
|Canelo open to GGG trilogy as he chases place in Mexican history|
|The big Friday Premier League quiz|
|Harden posts record fourth 50-point triple-double in win over Lakers|
|Barcelona squad happy with Dembele, says Alba|
|Chargers rally past Chiefs to clinch playoff spot|
|WATCH: Chargers top Chiefs on dramatic two-point conversion in final seconds|
|Suns owner Sarver committed to keeping team in Phoenix|
|Chargers WR Allen leaves with injury after near-spectacular catch|
|Socceroos not giving up on Mooy for Asian Cup|
|Cooper says Raiders owner wanted to trade him to Cowboys|
|Pochettino jokes Levy is ´worried´ about losing him|
|Barcelona would welcome Morata – Alba|
|Toure not a priority for West Ham – Pellegrini|
|Koscielny no certainty to face Southampton, says Emery|
|We gifted the game – AC Milan boss Gattuso furious after Europa League exit|
|My season starts now, says Koscielny|
|Cipriani ´at peace´ with latest England snub|
|Laporte: Deschamps must have personal reasons for France snub|
|Morata injury not too serious, claims Chelsea boss Sarri|
|Hansen to leave: All Blacks coach returning focus to World Cup defence|
|I want to fight the champion! - Joshua reiterates Wilder in April ambition|
|Gundogan glad to leave Christmas holidays behind|
|I know how it feels and it hurts - Gundogan on Sterling abuse|
|Celtic 1 Red Bull Salzburg 2: Scottish champions through despite defeat|
|Olympiacos 3 AC Milan 1: Rossoneri crash out of Europa League|
|Arsenal 1 Qarabag 0: Lacazette on target as Saka shines|