Halle, Germany, 7 June 2011 | AFP

Halle top seed Roger Federer has pulled out of the ATP Tournament, claiming he needs to rest after a gruelling French Open.

The 30-year-old Swiss, who was drawn to play Lleyton Hewitt in the opening round, made the decision just a day after losing to Rafael Nadal in four sets in the final at Roland Garros.

Hewitt, the defending champion at Halle, will now play a lucky loser in the opening round.

Federer confirmed the decision, claiming he did not want to risk aggravating his delicate groin ahead of Wimbledon later this month.

“My body and especially my groin need a rest after Roland-Garros,” he wrote on the tournament’s website.

In the on-court action on Monday, Taiwan’s Yen-Hsun Lu booked his place in the second round with a 7-6 (7-2) 6-3 win over Finland’s Jarkko Nieminen.

Lu, who reached the quarter-finals at Wimbledon last year, finally got into his stride in the second set but admitted the transition from clay to grass is no easy task.

“It was a tough match to start the grass-court season, I know Jarkko is very good on grass,” Lu said.

“We were both trying to find a rhythm and get a feel for the grass.

“It was a high quality match and I am glad I won, there are lots of positives to take.

“It’s not easy to switch from clay to grass, there is a lot of difference.

“You are using different muscles, the ball is a lot lower.

“I have had two days practice, I still have two more weeks (until Wimbledon), so there is plenty of time to get ready.”

Lu will play a German in the second round and faces either wild-card Dustin Brown or sixth-seed Florian Mayer.

“For sure, they will want to do well at home and they will have the crowd behind them,” said Lu.

“It will help them, but I can’t care about that, I have to focus on my game and not lose my concentration.”

Seventh-seed Alexandr Dolgopolov of the Ukraine is into the second round after he recovered from losing the first set tie-breaker to beat Holland’s Robin Haase 6-7 (4-7) 6-4 6-4.

Local favourite Philipp Kohlschreiber is also through after grinding out a 6-4 3-6 6-1 win over Cedrik-Marcel Stebe in just over two-hours.

In other results, Germany’s Tobias Kamke progressed to the second round after compatriot Julian Reister retired injured in the first set.

Russia’s Igor Andreev enjoyed a straight sets win over Potito Starace of Italy, while qualifier Jan Hernych of the Czech Republic made the second round with a hard-fought win in three sets against Sergiy Stakhovsky of the Ukraine.

Fourth-seed Mikhail Youzhny of Russia, who had been due to face Philipp Petzschner of Germany, has pulled out after suffering a foot injury and has been replaced in the draw by lucky loser Dominik Meffert of Germany.