Fatigue and injury have combined to curtail Daria Gavrilova's Kremlin Cup campaign - and dent the Australian's hopes of qualifying for the Elite Cup.
Gavrilova was forced to retire hurt from her second-round match against Vera Lapko, trailing 6-3 3-1 to the Belarusian qualifier in Moscow when she pulled the pin shortly after a medical time out.
With her left hamstring already heavily strapped, the 23-year-old received treatment on her right leg and after the world No.167 held serve to extend her lead, Gavrilova walked to the net and shook her opponent's hand.
The prestigious $US2.3 million Elite Trophy takes place in China from October 31 and features players ranked ninth to 19th and local qualifier Peng Shaui at the end of the WTA's 2017 points race.
US Open champion Sloane Stephens and fellow grand slam winners Angelique Kerber and Svetlana Kuznetsova have already qualified.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Gavrilova is 22nd and needed to at least reach the quarter-finals in Moscow - where she was runner-up last year to Kuznetsova - to directly qualify.
Ashleigh Barty, who is sitting out the tour this week, is currently 19th in the race after landing her maiden singles title and reaching two other finals in a breakout season.
Moscow-born Gavrilova has enjoyed the best season of her career, winning her first WTA tournament in New Haven, in August.
She has also reached two finals including last week's Hong Kong Open, losing a titanic three-hour decider to world No.18 Anastasia Pavlyuchenkova.
Less than 48 hours later, Gavrilova was on court against Kristyna Pliskova following a 10-hour flight to the Russian capital.
What looked to be a routine win over the Czech left-hander became a gruelling encounter before she finally prevailed 6-4 6-7 (7-5) 6-1 having squandered five match points in the second set.
Gavrilova then had to back up in the third match on the day on Wednesday and subsquently struggled throughout, gift-wrapping the biggest win of the young Belarusian's career.
"My body is very confused what time zone it's in?!?!?!?!?!?," Gavrilova Tweeted after the match.
Joining Lapko in the final eight is fellow Belarusian Aleksiandra Sasnovich, who took out top-seeded Frenchwoman Kristina Mladenovic 6-2 2-6 6-2.
It was a day when seeds tumbled. Second seed Coco Vandeweghe was knocked out 7-5 1-6 6-2 by Ukraine's Lesia Tsurenko and fourth-seeded Latvian Anastasija Sevastova was beaten 6-4 6-3 by Romania's Irina-Camelia Begu.
Julia Goerges is at this stage the sole seed through to the final eight after the German beat Yulia Putintseva 6-3 6-3.
