Thiem has definitely looked better this tournament, but anytime Djokovic has been pushed up against a wall this week he played incredibly, so I really can't say for sure who I think will win.
It was the second year running that Williams, seeded 10th and competing in her 20th French Open, lost to the Swiss in the Roland Garros fourth round even though she fought back from 5-1 down to rattle off six straight games to win the first set. In the women's section, former World No. 1 Caroline Wozniacki and French No. 1 Kristina Mladenovic play their quarter-final games today against Latvian Jelena Ostapenko and former French Open semi-finalist Timea Bacsinszky, respectively.
"I hope things are going well for him, and he's someone I really like".
Djokovic has all the running against Thiem, but in the grand scheme of things, it's Thiem's time to shine and he will put some strong form to good use. Since returning from the injury layoff earlier this year, the world number five has looked a different player and he has been unbeatable on the dirt.
And with the Austrian crushing Horacio Zeballos 6-1 6-3 6-1 in the fourth round, it's certain that he will provide a stiff test.
"I'm sad. It's a very painful defeat here in the French Open", said Muguruza, who left Court Suzanne Lenglen angrily wagging her finger at the crowd. Talking about his upcoming challenge against Dominic Theim, Djokovic said, "There's no easy match in a Grand Slam quarter-final, it will be very hard for both of us".
The Serb struggled in the opening set, twice fighting back from a break down to claim it on a tie-break.
Big-serving American John Isner, seeded 21, was knocked out in his third-round match by Karen Khachanov of Russian Federation, who won 7-6 (7-1), 6-3, 6-7 (5-7), 7-6 (7-3).
"Everything wasn't ideal. There were a few concerns", Mladenovic said, before joking: "I made about 35 double-faults today, but everything's OK!"
Eighth seed Nishikori led two sets to one but trailed by a double break at 3-0 down in the fourth set when rain halted play on Saturday.
The nine-time champion matched Roger Federer's record for quarter-final appearances at Roland Garros.
Second seed Karolina Pliskova advanced to round four with a 7-5, 6-1 victory over Germany's Carina Witthoeft.
The 30-year-old Monfils won 7-6 (7-5) 5-7 4-3 to set up a last-16 meeting with third seed Stan Wawrinka.