French Open 2017: Dominic Thiem defeats Novak Djokovic in straight sets to set up semi-final clash with Rafael Nadal

Paris: Novak Djokovic's French Open title defense ended with a surprisingly lopsided 7-6 (7-5), 6-3, 6-0 quarterfinal loss to sixth-seeded Dominic Thiem of Austria on Wednesday.

A year ago, Djokovic became the first man in nearly half a century to claim a fourth consecutive major championship and completed a career Grand Slam at Roland Garros. But his form has dipped considerably since then, and now he has gone four majors in a row without earning a trophy.

"It's a fact that I'm not playing close to my best," Djokovic said. "This is a whole new situation that I'm feeling."

On Wednesday at a windy Court Suzanne Lenglen, Djokovic was out of sorts in so many ways, even before that 20-minute third set in which he won only 8 of 34 points. That was only the second time that Djokovic lost a final set by the score of 6-0 in his 937 career tour-level matches.

"It was not there for me today," Djokovic said with a sigh.

He wasted two set points in the opener. By the end of the match, he wound up with nearly twice as many unforced errors, 35, as winners, 18. His backhand was particularly problematic.

Known for tremendous footwork and court coverage, the No. 2-seeded Serb even stumbled and tumbled to the court, his racket flying out of his hands, early in the second set. Djokovic was left on his knees, and soon he would be out of the tournament entirely.

"All in all, it was decided, I think, in the first set ", said Djokovic.

How unlikely was this result? Djokovic entered the day having won all five previous matches - and 11 of 12 sets - against Thiem, including in the French Open semifinals a year ago.

"It's amazing for me," Thiem said. "To beat him for the first time in the quarters of the French Open is a dream."

Plus, Djokovic had appeared in a record six consecutive semifinals in Paris. But this continued what has become something of a 12-month downward slide for him since he finally grabbed ahold of the French Open championship he had so long sought.

Since then, though, the highlight for Djokovic was a runner-up finish at the U.S. Open. Otherwise, he lost his No. 1 ranking to Andy Murray and lost in the third round of Wimbledon, the first round of the Rio de Janeiro Olympics, and the second round of the Australian Open.

Along the way, he split with one of his coaches, Boris Becker, and then his other, Marian Vajda, along with other members of his entourage. Djokovic enlisted Andre Agassi for coaching help during Week 1 of the French Open, but Agassi had some prior commitments and so was gone by the time Djokovic faced Thiem.

The 23-year-old Thiem will face nine-time French Open champion Rafael Nadal next.

"You have to play the best guys round after round," Thiem said. "It's not getting easier on Friday."

The other men's quarterfinals scheduled for later Wednesday: 2016 runner-up Murray vs. No. 8 Kei Nishikori, and 2015 champion Stan Wawrinka vs. No. 7 Marin Cilic.

Thiem is a talented, up-and-coming player, to be sure, and he is the only man to beat Nadal in the Spaniard's 23 matches on clay in 2017. That came in the quarterfinals of the Italian Open last month.

Earlier Wednesday, Nadal reached his record 10th French Open semifinal when No. 20 Pablo Carreno Busta of Spain retired from their match early in the second set because of an injured abdominal muscle he said began bothering him on a serve at 5-2 in the first.

Nadal led 6-2, 2-0 when Carreno Busta stopped.

Nadal has dropped only 22 games so far in the tournament, the fewest he has lost on the way to any of his 26 Grand Slam semifinal berths.

"I don't know how many games I lost this year, but I really don't care about this, no?" Nadal said. "I only care that I am in the semifinals."