French Open champion Rafa Nadal made a successful transition from clay to grass with a 7-5 6-1 win over Slovakia's Lukas Lacko 7-5 6-1 to join his great rival Roger Federer in the quarter-finals of the Halle Open on Thursday.

Spaniard Nadal, playing at Halle for the first time since a first-round exit in 2005, needed a little time to settle before overcoming Lacko in 76 minutes to set up a meeting with champion Philipp Kohlschreiber, who defeated Lukasz Kubot 6-7 6-1 6-3.

"At the beginning, it was more difficult to return," Nadal, who won a record seventh French Open title on Monday, was quoted as saying by the ATP website (www.atpworldtour.com).

"I tried to put more balls inside, trying to return with a bit of slice. That put me into a bit more of a rhythm.

"Every match here is very dangerous after playing on clay for 2-1/2 half months," he added.

Five-times champion Federer, who has the road leading to the tournament stadium named after him, won 6-4 7-5 against Florian Mayer to maintain his unbeaten record over the German having won their three previous matches.

"I'm very happy with the way things went today. I obviously knew playing against Mayer in the first round was going to be tricky," Federer said.

"He's in the top 30 and has been to the quarter-finals of Wimbledon. I've played him here on grass before, so I know how tough he can be."

Second seed Federer next faces Canadian Milos Raonic in the Wimbledon warm-up event.

(Writing By Alison Wildey in London; Editing by John Mehaffey)