Novak Djokovic’s tame straight-sets defeat to Dominic Thiem at the French Open has led observers to question what has gone wrong with the former world No 1.

The Serbian No 2 seed was second-best throughout to powerful-hitting Thiem, losing 7-6 (7-5), 6-3, 6-0 at Roland Garros in Paris.

It was the Austrian’s sixth seed’s first victory over Djokovic and he will now play Rafael Nadal in the last four.

Nadal reached the semis after fellow Spaniard Pablo Carreno Busta withdrew from their match with an abdominal injury while trailing 6-2, 2-0.

Fourth-seed Nadal is aiming to win a record 10th title at Roland Garros, having become just the fifth man to reach 10 semi-finals at a single Grand Slam in the Open era.

In 2016, Djokovic won the French Open title to become the first man since 1969 to hold all four Grand Slam titles at the same time.

Since then, the 30-year-old has lost in the third round at Wimbledon, suffered defeat in the US Open final, and lost in round two at the Australian Open. He has now failed to progress past the last eight in Paris for the first time since 2010.

‘This is a whole new situation for me, not winning a big tournament for eight or nine months – this hasn’t happened for a while,’ said Djokovic.

‘All the top players have gone through that and I have to learn lessons and figure how to get through. It is a big challenge and I’m up for it.’

However, former great John McEnroe was typically more blunt.

‘I don’t recall seeing a time in the last six to eight years when Novak mailed it in,’ McEnroe told BBC Sport.

The American, a seven-time Grand Slam singles champion, added: ‘He basically gave up.’

Djokovic won just eight points and made 12 errors in the final set of his quarter-final, which lasted 20 minutes.

It was only the ninth time he had lost a set to love in his career, and the first at a Grand Slam since he played Gael Monfils at the US Open 12 years ago.

‘It looked in the third set like he just didn’t want to be out there, couldn’t compete any more, and that’s shocking for a guy that’s won as much as he has and prides himself on competition,’ added 58-year-old McEnroe.

Elsewhere, Britain’s Andy Murray reached his fourth consecutive French Open semi-final with a four-set win over Kei Nishikori.

The world No 1 came through 2-6, 6-1, 7-6 (7-0), 6-1 against the Japanese No 8 seed at Roland Garros.

The 30-year-old goes on to face Swiss third-seed Stan Wawrinka, who beat Marin Cilic 6-3, 6-3, 6-1.

It is a repeat of last year’s semi-final, which Murray won in four sets before going on to lose in the final.

In the women’s draw, Simona Halep battled back to beat Elina Svitolina 3-6, 7-6 (8-6), 6-0 in the quarter-finals.

Third-seed Halep looked to be heading out after going a set and 5-1 down. But the Romanian won five consecutive games and then saved match point to take it to a decider, which she finished off with ease.

Halep will play Karolina Pliskova in the last four, after the world No 3 beat Caroline Garcia 7-6 (7-3), 6-4 in the other quarter-final.

Pliskova, 25, will replace Angelique Kerber as the new world No 1 if she beats Halep to make Saturday’s final.