After an impressive first set, Thiem kept up the pressure early on, breaking for a 2-1 lead and saving a break point to hold for 3-1.
Schwartzman-esque fightbacks are nothing new for Alexander Zverev, who has come back from 2-1 down in sets in his last three rounds to win deciding sets, and his court time is hugely in excess compared to his other rivals still in the competition. "This definitely paid off, the hours in the gym every day". I'm happy with all of my game.
Zverev, however, has spent 11 hours and 56 minutes on court in Paris but Thiem believes his rival will be fully fit.
"Physically, obviously it's not easy to play, you know, back-to-back-to-back five-set matches, but I will manage it somehow".
"The first two sets were unbelievable but then he raised his level and it was 50-50", said Thiem of Nishikori. Djokovic may not go on to win the tournament, but putting himself in the conversation to challenge for majors is something that will please him for now and he should book his place in the semi-final with a win here against Cecchinato.
Yes, Djokovic was thrilled to get back to a ninth consecutive quarterfinal in Paris after dealing with elbow trouble for more than a year and needing surgery in February.
"I am within the quarterfinals of a grand slam".
The 21-year-old German argued with the umpire over a line call before he eventually lost the first set to the Russian world No. 38.
Zverev bore a heavy weight of expectation coming to Roland Garros this year but has taken the hard path to the French Open quarters as he came back from a set down to beat Khachanov 4-6, 7-6 (4), 2-6, 6-3, 6-3. He then patted Khachanov, a friend from their junior days, on the chest before pumping his arms to celebrate.
The second set was another struggle for Zverev, who had three set points while serving at 5-4 only for Khachanov to save them all and get the break a few points later. He then needed four sets to overcome the talented Greek teenager Stefanos Tsitsipas and also dropped a set against Italy's Matteo Berrettini, winning 6-3 6-7 6-2 6-3. An ace gave him another set point but he also missed that one, putting a low volley into the net.
Djokovic saved three match points in the fourth-set tiebreaker before his 72nd-ranked rival converted his fourth with a backhand return victor.
At 2-2 within the fourth, Zverev saved two break factors after which broke for 4-2 after Khachanov led 40-15 on serve.
The win was the seventh-seeded Thiem's first over Nishikori in three career matches. "Hopefully big things can happen here".
The 12-time grand slam winner's subsequent challenger is not David Goffin however fairly Marco Cecchinato, who upset the ailing eighth-seed 7-5 4-6 6-Zero 6-Three after shedding to the Belgian final month.
Thiem was asked before their quarter-final what he expected of the match.