HAMBURG, Germany (AFP) - Claycourt king Rafael Nadal booked his place in the quarter-finals of the Hamburg Masters on Thursday to spoil British number one Andy Murray's 21st birthday celebrations.

World number two Nadal needed just over an hour to see off 15th seed Murray 6-3, 6-2 and set up a quarter-final clash against compatriot Carlos Moya on Friday.

This was the third time Murray has met - and lost - to Nadal and there was little for the Scotsman to celebrate on his landmark birthday.

"His forehand is incredible on clay, I think it's one of the best in tennis," said Murray.

"I had my chances against him, but with a guy like that he is virtually unstoppable once he goes on the front foot."

With his grandmother watching in the stands here - as she did last season when he badly injured his wrist - Murray said he was looking forward to celebrating his birthday with his family.

"But I might try and keep gran away next year, so I might have a chance of winning," he quipped.

Having struggled in his second round win over Italy's Potito Starace on Wednesday, Nadal said he was happy with his performance and the blisters which blighted him last week in Rome have healed.

"My game was 50 percent better, the foot is better, I practiced a lot before this game and it showed," said Nadal.

Defending champion Roger Federer and world number three Novak Djokovic are also in the last eight while Nicolas Kiefer became the first German this century to make the quarter-finals.

Before Kiefer's third-round upset of fourth-seed Nikolay Davydenko, Tommy Haas at the 1999 tournament had been the last German to achieve the feat.

Kiefer's 7-5, 6-3 win over the Russian means there will be huge support in the Am Rothenbaum stadium for Friday's quarter-final against Italy's Andreas Seppi.

Kiefer, 41 in the ATP rankings, came out on top against the world number four after one hour and 54 minutes having also beaten last week's Rome finalist Stanislas Wawrinka in the second round.

Federer won his third round clash against Sweden's Robin Soderling 6-3, 6-2 in just one hour six minutes.

"I was happy with the match, I controlled things well from the baseline and I feel comfortable here," said Federer who has won four of the last six tournaments in Hamburg.

"I have been doing well here since 2002, I struggled for a few years before that, but I have had so much success here since then. Germany is similar to Switzerland and it helps to be in familiar surroundings."

Having beaten Nadal in last year's final, Federer will now meet Spain's Fernando Verdasco in Friday's last eight.

Australian Open winner Djokovic, who set up a quarter-final clash with Spain's Albert Montanes, is on course to meet Nadal if the pair both make it to Saturday's semi-finals.

Djokovic had few problems as he saw off Croatian giant Ivo Karlovic 7-6 (7/3), 6-3.

"It's never easy to play Karlovic," said the 20-year-old.

"We all know he has one of the best serves on tour, but I was happy with the way the match went.

"I don't know much about Montanes, but he must be a quality player if he can get this far in this competition. He has nothing to lose and I will have to be aggressive to get the win."

Earlier, seeded pair Argentine Juan Monaco and Spain's David Ferrer both crashed out.

Italy's Seppi made the last eight after he removed his second consecutive seed from the draw with a 6-0, 6-3 win over 12th seed Monaco.

And fifth seed Ferrer went out when he was beaten 7-6 (7/4), 6-2 by Verdasco.