Despite all this, Thiem remained rock solid on the other side of the net, and though Zverev was able to hold for 5-2, Thiem comfortably served out the second set to take complete control of the match.
Cut to the women's fourth round, where Keys beat Buzarnescu 6-1, 6-4 despite showing some wobbling signs in the second set. Thiem defeated Zverev twice more during that clay court season, in the final in the warm-up event in Nice 6-4 3-6 6-0 and in the Roland Garros third round 6-7 6-3 6-3 6-3.
He will be wary of Cecchinato, though, after the Italian world number 72 produced a sensational display to down Djokovic.
He said: "I'm not concerned". "It will be a pleasure to play against Novak".
For the former champion, though, it was not to be as he came up against the unseeded Marco Cecchinato in blistering form, and lost a gruelling and highly intense four-setter, 6-3, 7-6 (4), 1-6, 7-6 (11).
Keys said she was looking forward to Monday's blockbuster between Maria Sharapova - they share the same agent, Max Eisenbud - and Serena Williams.
The Williams sisters have claimed 14 Grand Slam doubles titles together since winning the French Open title in 1999, but bowed out at the last-16 stage this year.
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Djokovic continued his solid progress too as he powered to a 6-2, 6-4, 6-2 win over Spain's Fernando Verdasco, and the Serb says he knows Cecchiato quite well.
The 23-year-old will next face U.S. Open runner-up Madison Keys. He was also a French Open semi-finalist the past two years. "[At the] beginning of the fourth set I thought, okay, I can turn this match around, especially when I saved a few break points".
"The first two sets were incredible but then he raised his level and it was 50-50", said Thiem of Nishikori. "Bodily, clearly it isn't simple to play again to again to again five-set matches, however I'll handle it in some way". It's something very special to serve for the French Open quarters.
Alexander Zverev of Germany (right) shakes hands with Karen Khachanov of Russian Federation after winning their men's round of 16 match during the French Open tennis tournament at Roland Garros in Paris, France.
Unfortunately the match-up was ruined as a contest when Zverev, playing his first Grand Slam quarter-final, pulled his left hamstring midway through the second set.
"I'm young, so I might as well stay on court and practise a little bit", Zverev said. At 9-8, Djokovic flubbed a forehand, knelt and clasped his hands together as if praying, then raised an index finger as if to plea, "Let me have ONE of these!" "This definitely paid off, the hours in the gym every day".
"I'm a better player in general, for sure." said the world number eight, who barely put a foot wrong in a one-sided quarter-final.
Cecchinato (it's pronounced cheh-key-NAH'-toe) came through on his fourth match point, looping in a backhand return victor as Djokovic tried to surprise him with a serve-and-volley attempt.