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.
|Dramatic Dovizioso crash gifts Marquez MotoGP title in Japan|
|LeBron´s home debut ends in defeat, Walker makes NBA history|
|Rondo, Ingram and Paul exchange punches in Lakers-Rockets clash|
|Dodgers to face Red Sox in World Series after beating Brewers|
|Valverde doesn´t care about extending Barca contract|
|Qualifying speed a ´positive surprise´ for Ferrari´s Vettel|
|I was in a different headspace – Hamilton revels in Austin pole|
|Barcelona can cope without Messi – Pique|
|Allegri: Juventus abandoned Genoa clash|
|Sale: Hospital visit was because of belly button ring|
|Valverde accepts Barcelona will miss Messi|
|No Messi or Ronaldo in El Clasico for first time since 2007|
|Barcelona have not won a Clasico without Messi since his debut|
|Ramos calls for Real Madrid unity after latest loss piles pressure on Lopetegui|
|Hamilton has title in sights after storming to Austin pole|
|Inter, El Clasico and more - the games Messi will miss with broken arm|
|End of Messi-Ronaldo duel good for LaLiga - Simeone|
|Messi out of Clasico with fractured arm|
|Awesome Ashton marks Sale bow with hat-trick|
|Klopp hopes for positive Henderson prognosis amid Liverpool injury issues|
|Benitez ´convinced´ Newcastle can survive despite seventh defeat|
|Barcelona 4 Sevilla 2: Messi injured but champions go top|
|Kovac relieved by Bayern´s timely victory|
|Strasbourg 2 Monaco 1: Sy howler and Grandsir red card cost Henry in first match|
|Leicester City defender Chilwell signs new six-year contract|
|PSG´s Tuchel hopes Verratti and Di Maria can face Napoli|
|Liverpool star Salah had no fear during scoring drought|
|Alonso´s 2019 plans not damaged by McLaren´s IndyCar decision|
|Edinburgh outclass troubled Toulon, Wasps and Bath play out thrilling draw|
|Barca concern as Messi substituted with worrying arm injury|
|Howe: South coast derby draw a fair result|
|Our heads were in Manchester – Allegri left fuming at Juventus´ loss of focus|
|Derby County 2 Sheffield United 1: Marriott blunts Blades with 77th-minute winner|
|We have so many problems – Jokanovic alarmed by Fulham defensive woes|
|Huddersfield Town 0 Liverpool 1: Salah snaps winless streak|
|Pellegrini ruing injuries after Yarmolenko hurts ankle|
|Villarreal 1 Atletico Madrid 1: Simeone´s side denied LaLiga top spot|
|Gracia: Not easy to dominate Wolves like that|
|Isner´s Finals hopes hindered by Stockholm defeat|
|Dyche incredulous at refereeing decisions in Man City thrashing|
|Juventus 1 Genoa 1: Champions´ winning run ends despite record Ronaldo goal|
|´Fantastic´ Lamela urged to find consistency by Pochettino|
|You don´t want to lose any players - Young speaks out on Wade NFL speculation|
|Championship Review: Smith gets off to a winning start, Leeds beaten|
|Guardiola hails extraordinary Fernandinho after Burnley drubbing|
|Pochettino lauds Lloris as one of world´s best after West Ham heroics|
|Paris Saint-Germain 5 Amiens 0: Ten wins in a row for PSG as Neymar rests|
|Cristiano Ronaldo nets record 400th league goal|
|Marcelo backing beleaguered Lopetegui despite Madrid slump|
|Garcia dazzles to hit the front at shortened Valderrama Masters|
|Cardiff City 4 Fulham 2: Paterson gets Bluebirds off the mark|
|Newcastle United 0 Brighton and Hove Albion 1: Benitez´s men bottom after dismal defeat|
|West Ham 0 Tottenham 1: In-form Lamela settles London derby|
|Manchester City 5 Burnley 0: De Bruyne returns in comfortable win|
|Wolves 0 Watford 2: Capoue and Pereyra turn form book on its head|
|Bournemouth 0 Southampton 0: Howe´s side stifled by Saints|
|Prove you´re crazy about Inter - Spalletti rallies players ahead of Milan derby|
|Wolfsburg 1 Bayern Munich 3: Lewandowski leads Kovac out of trouble|
|Goerges betters Bencic to clinch Luxembourg title|
|Morgan wants more from ´rusty´ England despite series win|
|Sarri says sorry after touchline bust-up overshadows Chelsea´s late escape|
|Chelsea draw an ´awful´ result for excellent United, says Mourinho|
|The Chelsea assistant that angered Mourinho - Who is Marco Ianni?|
|Steve Kerr supports Colin Kaepernick: ´I think he deserves a chance to play´|
|Lopetegui ´more motivated than ever´ amid Real Madrid sack reports|
|That´s football – Rudiger shrugs off late Ianni-Mourinho fracas|
|AC Milan´s improved mentality could be difference against Inter - Gattuso|
|Emotional Kasatkina comes back from the brink to win Kremlin Cup|
|Forget it, it´s over - Mourinho accepts apology over touchline row|
|Mourinho in furious bust-up with Chelsea staff after late equaliser|