"In two days' time I will be playing in the quarter-finals here, and I'm happy about that", said the German, after fighting back from two sets to one down for the third straight match by beating Khachanov 4-6, 7-6 (7/4), 2-6, 6-3, 6-3.
Zverev, whose previous Grand Slam best was reaching the fourth round at Wimbledon past year, said he spends up to four hours each day working on weights and fitness in the gym.
American 13th seed Madison Keys also reached her first Roland Garros quarter-final with a 6-1, 6-4 win over Romania's Mihaela Buzarnescu.Keys, the US Open runner-up to Stephens previous year, will face Kazakhstan's Yulia Putintseva for a place in the semi-finals, after the world number 98 saw off Barbora Strycova 6-4, 6-3. After dropping serve to trail 4-1 Zverev called for the trainer and had a bandage applied to his left leg - hardly surprising considering the way he had been moved around by his close friend. Zverev had needed five sets to beat Dusan Lajovic, Damir Dzumhur and Karen Khachanov and his first-week graft caught up with him on a damp and cool Tuesday. "I'm very happy about being in the quarterfinals here, going the hard way, going the long distance ... showing everybody that I can play for as long as I need to".
"He's playing this year an incredible year, match after match, so I don't think and I don't expect him (to be) exhausted". But he recovered to win the 4th set. "I love it here and I will do everything to make one more step this year".
Cecchinato dropped the opening two sets that day against someone named Marius Copil, a Romanian ranked 94th, and then was two points from losing, right then and there.
He won just four points as Thiem raced 4-0 ahead, fighting back briefly by earning a break point at 4-1, but losing serve again in the next game as Thiem advanced with a trademark backhand victor.
When the match ended on court docket Suzanne-Lenglen, Zverev sunk to his knees with arms outstretched.
A thumping 135mph ace out wide wrapped up a one-set lead for the 24-year-old, who looked assured and dominant on serve.
Cristiano Ronaldo makes 'irreversible decision to leave Real Madrid'
Ronaldo is ready to leave the Santiago Bernabeu this summer as the club hierarchy are unwilling to pay him what he is demanding. Bale was deeply impacted by Zidane's decision to not to start him more often in his final few months at the club.
"I think that's the matchup most of the fans in Germany and Austria were hoping for when they saw the draw", he said.
Khachanov had some chances in the second and again late in the match, but his forehand let him down. Cecchinato had never won a match at a major tournament until last week and, at No. 72, is the lowest-ranked French Open men's quarterfinalist in a decade. But Cecchinato came all the way back, winning 10-8 in the fifth set.
He said: "I'm not concerned".
Men's fourth round: No. 1 Rafael Nadal beat Maximilian Marterer 6-3, 6-2, 7-6 (4); No. 3 Marin Cilic beat No. 18 Fabio Fognini 6-4, 6-1, 3-6, 6-7 (4), 6-3; No. 5 Juan Martin del Potro beat No. 9 John Isner 6-4, 6-4, 6-4; No. 11 Diego Schwartzman beat No. 6 Kevin Anderson 1-6, 2-6, 7-5, 7-6 (0), 6-2.
"For me, " he continued, "this is the best moment of my life".
Both Zverev and Thiem, who were dubbed as two of main threats for Nadal at Roland Garros 2018, have been making heads turn with their performances on clay-court over the last few seasons. "And we actually trained this year before Monte-Carlo tournament".
"Then, you know, each game and each slide, I was getting worse and worse. I played a lot".
"Maybe it gets a little bit easier in the future when they are not that young anymore or when some of them stop".