PARIS -- Novak Djokovic is into his record 10th consecutive French Open quarterfinal, something not even the king of clay, Rafael Nadal, has managed to do.
And Djokovic is yet to be challenged this year at Roland Garros. Not only hasn't he lost a set -- he has only twice ceded as many as four games in a set.
Extending his Grand Slam winning streak to 25 matches and closing in on a fourth championship in a row, Djokovic was dominant yet again in the fourth round Monday, beating 45th-ranked Jan-Lennard Struff of Germany 6-3, 6-2, 6-2.
"Everything is coming together beautifully. I'm motivated to fight for the trophy, yes. I mean, that's why I'm here," said Djokovic, who owns 15 Slam titles, including one in Paris. "But it's still a long way to go."
It has helped, certainly, that the No. 1-ranked Djokovic has not needed to deal with a seeded foe yet. That will change now: He faces No. 5 Alexander Zverev for a spot in the semifinals.
Have things been too easy so far? Is it possible that Djokovic hasn't had the proper preparation for what could be tougher going in the latter portion of the tournament?
"I don't mind cruising along, to be honest," he said with a smile. "I have plenty of experience, I think, dealing with situations where you're facing break points or where it's tense. I have played plenty of, I think, tight matches in my career, that I can rely on that experience."
He added: "It's good to be tested, from that perspective, but at the same time, it's also good to cruise along and kind of conserve the energy for what's coming up."
Djokovic and Zverev have split four previous tour meetings.
Zverev reached his second straight quarterfinal in Paris by coming back to eliminate No. 9 Fabio Fognini 3-6, 6-2, 6-2, 7-6 (5).
He's only 22, but Zverev has been touted as a future champion for quite some time. He has yet to play in a major semifinal, though, and mentioned Monday that he enjoyed getting to be a bit under the radar so far in this French Open, noting that 20-year-old Stefanos Tsitsipas, the sixth seed, was a subject of more focus until losing in the fourth round to Stan Wawrinka.
"For me," Zverev said, "it was actually quite a nice thing that not all of the attention ... is only going towards my way."
Unlike Djokovic, he has not exactly had an easy path to the round of eight: Zverev needed to win two five-setters in addition to going four against Fognini.
In other matches, Kei Nishikori of Japan won his eighth consecutive five-set match on Monday, defeating Benoit Paire 6-2, 6-7 (8), 6-2, 6-7 (8), 7-5 over two days and set up a quarterfinal match against defending champion Nadal.
In a match ridden with unforced errors that featured 15 breaks of serve but also some beautiful shots, Nishikori prevailed after a nearly four-hour battle. Their fourth-round match had been suspended by darkness on Sunday, with Nishikori leading two sets to one.
Nishikori extended his impressive record in five-set matches to 23-6, including a 6-1 mark at the clay-court Grand Slam. He also holds the best percentage of wins in deciding sets (132-45, .746) -- either in best-of-five or best-of-three matches -- since the Open era began in 1968.
In damp conditions, Paire's all-risk tennis was working when they came back on court. The Frenchman saved two match points in the fourth-set tiebreaker and served for the match at 5-3, but he was finally made to rue his mistakes.
"He was serving for the match, and I just tried to play one point at a time," Nishikori said.
Paire hit 15 double-faults and 79 unforced errors.
"Never easy to finish a match," Paire said. "It was tough emotionally. I'm very sad to lose this match but glad for what I did this week."
Nishikori will play in a third quarterfinal match in Paris but faces a tall order in the next round. Nadal has won 10 of their 12 previous matches, including all three matches on clay.
Last year's runner-up, Dominic Thiem, ended French hopes of Roland Garros glory by ousting Gael Monfils, the last Frenchman remaining in the draw, 6-4, 6-4, 6-2.
Monfils had not dropped a set in his three previous matches but could not find an answer to his opponent's consistency. Thiem produced a superb winner in the third set when, after being dragged to the net, he chased a backhand toward the baseline and fired a winner between his legs.
"He was just stronger; he impressed me a lot today," Monfils said.
Thiem will face 10th-seeded Karen Khachanov a 7-5, 6-3, 3-6, 6-3 winner over No. 8 Juan Martin del Potro.
Khachanov pointed to his pregnant wife in the stands after reaching his first Grand Slam quarterfinal.
The Russian told his support team in an on-court interview, "Let's go for more."
Information from The Associated Press was used in this report.