Time for Thiem or will Nadal march on?

Only one player has beaten Rafa Nadal on his beloved claycourts this year and that man, Austria's Dominic Thiem, blocks the Spaniard's path to the French Open final.

Not only that but sixth seed Thiem has not dropped a set en route to Friday's semi-final and on Wednesday trounced defending champion Novak Djokovic 7-6 6-3 6-0.

So, while many are already writing Nadal's name on the trophy for an unprecedented 10th time, the fourth seed will have some doubts in the back of his mind as he takes on a man aiming to avoid a second successive semis-final exit.

Nadal dropped 22 games in reaching the semi-finals -- the lowest total in the professional era -- but is unlikely to beat Bjorn Borg's record of dropping a mere 27 on his way to the 1978 final at Roland Garros.

Whether or not 23-year-old Thiem can win enough games to seriously worry Nadal will boil down to how much belief the Austrian can take on to the Philippe Chatrier court that Nadal has more or less owned since 2005.

What will help is the win he enjoyed over Nadal in Rome after losing to the 31-year-old in Barcelona and Madrid.

"It's great for me to be in the semi-finals again," Thiem said. "On Friday I'm playing the toughest opponent ever here in Roland Garros. The toughest match what you can imagine.

"But there are no secrets."

While Nadal, trying to become the second man in the professional era to make 10 appearances in the final at one grand slam after Roger Federer (Wimbledon), will be favourite to beat Thiem, the other semi-final looks too close to call.

It is a repeat of last year's semi-final when Andy Murray produced arguably his greatest match on clay to defeat reigning champion Stan Wawrinka.

World number one Murray is the only one of the surviving quartet to have been seriously tested so far here, having dropped three sets.

But after arriving in Paris at a low ebb after a poor run on clay, the arrival of coach Ivan Lendl to watch over his shoulder has flicked a switch and he looks menacing again.