STUTTGART (TIP): Top seed Rafael Nadal and Gael Monfils both struggled on their least-favourite surface Friday before setting up a semi-final at the first edition of the Stuttgart Open to be played on grass.

The former July clay-court tournament is now part of the three-week run-up to Wimbledon after being approached three years ago to consider making the drastic change of surface and date.

Nadal needed almost two and a half hours to defeat fifth seed Bernard Tomic 6-4, 6-7 (6/8), 6-3, defeating the Australian for the third time as they played on grass for the first time.

The Spaniard has now taken six sets and almost five hours on court to win two matches as he struggles to make the switch of surfaces.

He could have been home a winner in straight sets after going up a break in the second set and against holding a 4-2 lead in the tiereaker eventually won by Tomic which forced a final set.

Nadal scrapped through to victory but only after saving two break points in the seventh game of the thrd set and coming through on his second match point a game later.

Monfils fired 17 aces in a 7-5, 3-6, 6-3 quarter-final victory over Philipp Kohlschreiber which left Germany with just one title contender remaining.

Monfils was a former runner-up at the Weissenhof club on clay.

The defeat of Kohlschreiber, who played the 2013 final, leaves Mischa Zverev as the last home hope. He will aim for a place in the semis against second-seeded US Open winner Marin Cilic.

The last time a German lifted the trophy was 1991, when Michael Stich defeated Alberto Mancini.

Monfils struck for his 10th win over Kohlschreiber against just two losses –the German won their grass-court semi-final in Halle in 2011 and also put out Monfils on the Stuttgart clay in 2013.

The Frenchman got off to an early break of serve in the third to ensure victory after just under two hours on court in temperatures of 30 Celsius.

“I had some good luck today, I tried to play aggressive on returns and stick to a simple game plan,” said the winner, who admits that he will never put grass at the top of his favourite surface list.

“I know the grass now but I came here knowing that I had to work. Playing on this surface is never easy for me.

“My main goal is to keep form getting injured and try to do my best. If I can win some matches, that’s even better.