World number one Jelena Jankovic survived a scare before reaching the Kremlin Cup quarter-finals with a 6-7, 6-3, 6-2 win over Vera Dushevina on Thursday.
The Serb, who replaced Serena Williams at the top of the WTA rankings on Monday, was in danger of becoming the third high-profile player to bow out of the $2.3 million tournament.
Jankovic, making her Moscow debut, lost the first set and was 0-2 down in the second before finding her range to subdue the 77th-ranked Russian.
Jankovic said she had been ready to quit the match after losing her serve early in the second set.
"I just couldn't do it anymore at that point as I felt a pain in the back," she told reporters.
"I was ready to shake hands and finish the match but I said to myself, 'Just try every point, try your best'.
"I don't know how I managed to win today," she said.
Dushevina, 22, was unhappy with the way her opponent had conducted herself during the match.
"You always have to be on guard playing Jankovic because you never know what's going to happen with her," said the Russian. "She always complains that she has pain in her arm or leg or back or whatever.
"Today in one of the games on her serve she threw her racket and went to the bench calling for a trainer. Then she comes back and hits an ace, I don't think it's good sportsmanship. And she always argues with umpires."
The women's field, billed as the strongest in the Kremlin Cup's 19-year history with most of the world's leading players taking part, is already without ousted Wimbledon champion Venus Williams and French Open winner Ana Ivanovic.
Jankovic, fresh from winning her third title of the year in Stuttgart on Sunday, now faces unseeded Italian Flavia Pennetta, who followed her victory over Williams on Tuesday by beating Russian Ekaterina Makarova 3-6, 6-4, 6-4.
Earlier, seventh-seeded Russian Vera Zvonareva crushed Daniela Hantuchova 6-1, 6-0, setting up a quarter-final duel with another unseeded Slovak, Dominika Cibulkova, who upset Ivanovic on Wednesday.
Russia's Nadia Petrova also advanced after Caroline Wozniacki retired because of breathing problems. The Danish teenager had her blood pressure checked late in the first set before calling it quits while trailing 6-4, 3-2.
Men's top seed Nikolay Davydenko, bidding for his third Kremlin Cup title in a row and fourth in the last five years, also barely broke sweat, easing to a 6-1, 6-1 victory over Spaniard Guillermo Garcia-Lopez.
The Russian world number five will now take on his Davis Cup team mate, seventh seed Marat Safin, who prevailed over Julien Benneteau of France 6-4, 0-6, 6-2.
Safin said he would face little pressure against Davydenko.
"I have nothing to lose," said the former world number one.
"Nikolay is the one who has to feel the pressure because he is chasing a spot in the season-ending Tennis Masters Cup in Shanghai. But he is playing real well right now so I don't think I'll have much of a chance against him but I'll try anyway."