World number 38 Khachanov has now lost at the last-16 stage at Roland Garros twice in a row, while Zverev ended his wait for a maiden major last-eight appearance at the 12th attempt. Up next, will be a tasty quarterfinal showdown against Dominic Thiem.
Khachanov had some chances in the second and again late in the match, but his forehand let him down. Their quarterfinal on Court Suzanne Lenglen was later Tuesday.
The Serb, three-times a Wimbledon champion, appeared distraught after his quarter-final defeat by unseeded Marco Cecchinato in which he was treated for neck pain.
"I can last very long". "I wish to be residence proper now".
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.
And in typical Zverev model, he commendably vowed to be "prepared" for his crunch conflict with Thiem. "Going the hard way, going the long distance every single time and, you know, showing myself, showing everybody that I can play for as long as I need to".
"It's great to reach the semi-finals for a third year but it's time to take another step and I will do everything for that". Middle of the second set, the pain was too much. Nishikori came close to holding serve in the seventh, when Thiem had a triple break point, but the 19th-seeded Japanese star could not hold the Austrian off.
Thiem also took revenge on his German opponent following his loss in last month's ATP Madrid Masters final.
"It's, I think, the match, especially in Germany and Austria, everybody was hoping for".More news: Designer Kate Spade suffered from mental illness for years, sister says
Despite their relative youth, Zverev and Thiem have already faced off six times in their careers in a head-to-head that the Austrian leads four matches to two. "He is exclusively 21".
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In July 2016, Cecchinato was one of three Italian players initially suspended by their national tennis federation for allegedly influencing the outcome of matches.
Stephens will face Keys in an all-American battle for a spot in the French Open final.
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.
Visit the Roland Garros website for the results in full.
"I am clearly a tennis fan similar to everybody else, so I believe I am simply as excited to see that match", mentioned Keys.
The Serbian 12-time Grand Slam victor stepped it up a gear in the third and overwhelmed Verdasco with grueling groundstrokes to kill the match in two and a half hours.