LONDON: Wimbledon champions Roger Federer and Serena Williams were on course for further success at the All-England Club after booking their places in the Olympic singles semi-finals on Thursday.

World number one Federer will face Argentina's Juan Martin Del Potro for a place in the final, while Williams takes on top women's seed Victoria Azarenka in a repeat of her Wimbledon semi last month.

The two other semi-finals will pit Beijing bronze medallist Novak Djokovic against number three seed Andy Murray, and Russia's Maria Kirilenko faces her team mate Maria Sharapova.

Federer secured his place in the last four with a 6-4 7-6 win over America's John Isner, snatching victory in the second-set tiebreak with a cheeky shot which bounced off the top of the net.

“You just feel bad really. But relief because it's finally over... maybe I just got really lucky today,” Federer told reporters.

“I don't want to say that I feel invincible right now, but I feel good,” he added. “I'm not the only guy with confidence ...It's a complete open tournament, I think. Everyone has a very good chance of going all the way.”

Del Potro, who beat Federer in the US Open final in 2009, overcame Japan's Kei Nishikori 6-4 7-6 for his spot in the last four.

“I am very happy to be in the semi-finals in my first Olympic Games. It is amazing. I don't have too many words to explain this moment,” the eighth seed said after his win.

EXHAUSTED TSONGA

Second seed Djokovic dropped just one game in the first set of his quarter-final clash with France's Jo-Wilfried Tsonga, who was exhausted from playing in both the doubles and singles on Wednesday after clocking up the longest three-set match in Olympic history a day earlier.

Although the Frenchman took a 3-1 lead in the second, five-times grand slam winner Djokovic clawed it back to win 6-1 7-5.

Watched by Prince William and his wife Kate, Britain's Murray eased to a 6-4 6-1 win over injury-troubled Spaniard Nicolas Almagro, who received treatment on his right arm and shoulder after the first set.

In the women's event Belarusian Azarenka booked her place in the final four with a 6-4 7-5 win over Germany's Angelique Kerber.

Russia, which made a clean sweep of the women's singles medals in Beijing, can be sure of taking home at least one in London, with Sharapova and Kirilenko both through to the semi-finals.

The pair will play each other for a spot in the final after number three seed Sharapova ended Kim Clijster's hopes of an Olympic medal before her planned retirement later this year, beating the Belgian 6-2 7-5.

Having been broken in the second set, a valiant Clijsters battled back to level the score but was broken again and, with the Russian serving for the match, the Belgian ploughed a backhand into the net to hand her opponent the victory.

RUSSIA MEDAL

“Kim is so experienced, I knew that it would be really tough... it was such a tight second set, I was just happy to get through this one,” Sharapova told reporters, excited that a Russian would reach the final.

“No matter who's there someone will be getting a gold or silver medal. It makes me really happy that one of us will represent our country in the finals, going for gold,” she added.

“It's a pretty great honour not just to be here but to have a chance to win a gold medal. We're so happy.”

Number 14 seed Kirilenko overcame Czech former Wimbledon champion Petra Kvitova 7-6 6-3, while American Williams made light work of Denmark's Caroline Wozniacki, dismissing the eighth seed 6-0 6-3.

Kirilenko and Williams will both have a second semi-final to play on Friday when they face each other in the women's doubles.

Two-times doubles gold medallists Venus and Serena Williams play Kirilenko and her partner Nadia Petrova after the Americans knocked out second-seeded Italians Sara Errani and Roberta Vinci 6-1 6-1 in less than an hour.

The United States also has a shot at a medal in the men's doubles after top seeded brothers Bob and Mike Bryan secured their semi-final spot with a 7-6 7-6 win over Israel's Jonathan Erlich and Andy Ram, who ousted defending gold medallists Federer and Stanislas Wawrinka.

The Beijing bronze medallists will play Julien Benneteau and Richard Gasquet on Friday after the Frenchmen beat third-seeded Serbians Janko Tipsarevic and Nenad Zimonjic 6-4 7-6.

“It would mean everything to get a gold,” said Mike Bryan.