(CNN) -- American Venus Williams was the biggest name to head out of the Olympics tennis tournament in Wednesday's third round, losing 6-7, 6-7 to German Angelique Kerber.
Venus, the gold medal winner at the 2000 Sydney Olympics, struggled to cope with the intelligent play of Kerber.
The 24-year-old is enjoying the best year of her career, seeing her ranking rise to seven, and never looked in trouble against the seven time slam winning American.
Serena Williams, Venus' younger sister, didn't encounter the same problems as she swatted aside 2008 silver medal winner Vera Zvonareva 6-1, 6-0. The recent Wimbledon champion looked in imperious form, hitting 32 winners to her opponents three.
"I think I played better today and even in my second round than any match I played at Wimbledon," Williams said.
"I was just playing unbelievable. I felt good. I was relaxed. I felt like, you know what, I'm here to have fun, I have nothing to lose. No pressure on myself."
In the men's tournament, Roger Federer continued his quest to claim the only major title to elude him with a 7-5, 6-3 win over Uzbekistan's Denis Istomin. The Uzbek player threatened Federer at 5-5 in the first set, but the world number one snuffed out the threat relatively easy. From there on, the most successful tennis player of all time looked comfortable.
"I was happy with the way that I was able to turn it around," said Federer.
"Denis, I thought, played a very good first set; I didn't play poorly to let him back into the match. In the second set I guess I learned from the first set and was able to bring it home, so I'm very happy."
Federer will play the John Isner in the quarter finals after the big-serving American beat Serbia's Janko Tipsarevic 7-5, 7-6.
Not everything went Federer's way though, as later in the day he and Stanislas Wawrinka relinquished their Olympic doubles title to the Israeli pairing of Andy Ram and Jonathan Erlich.
Elsewhere in the doubles, Brazilian team Marcelo Melo and Bruno Soares won an epic encounter with Thomas Berdych and Radek Stepanek of the Czech Republic. The final set finished 24-22 in 191 minutes making it the longest set in an Olympic men's doubles match, and the match the longest three-set Olympic men's doubles match ever.
Federer's main rivals for Olympic gold both endured a difficult day at Wimbledon.
Novak Djokovic met former world number one Lleyton Hewitt in a gruelling encounter that ended 4-6, 7-5, 6-1 in the Serbian's favor.
Djokovic will face the dangerous Jo-Wilfired Tsonga in the next round after the powerful Frenchman beat Feliciano Lopez 7-6, 6-4.
Lopez is only in the singles competition after Spanish number one Rafael Nadal had to withdraw from the competition due to injury.
Local favorite Andy Murray also has hopes of winning a medal, having lost in the final at the recent Wimbledon Championships. He met the talented Cypriot Marcos Baghdatis in front of a raucous home crowd, producing a nervous 4-6, 6-1, 6-4 win.
"I was pretty unsure of myself at the beginning of the match, I didn't feel comfortable on the court," Murray told the Wimbledon website.
"Then I managed to settle myself down and move my feet better to get in better position in the second set. I played some good tennis after that."
Murray plays Spain's Nicolas Almagro in the quarter finals after the Spanish clay court specialist beat Steve Darcis 7-5, 6-3.
Former U.S. Open champion Juan-Martin Del Potro progressed to the quarter finals after recovering from an early scare against Giles Simon of France. Simon, renowned for an unrelenting game, looked to be struggling to match Del Potro's power when he lost the first set 6-1, but he recovered to take the second 6-4. The Argentinian Del Potro recovered his composure to seal the final set 6-3.
In the final men's match of the day, Japan's Kei Nishikori shocked number four seed David Ferrer of Spain with a 6-0, 3-6, 6-4 defeat. The match began on a packed court 14, but was moved under the Centre Court roof to ensure match was completed on Wednesday.
French Open champion Maria Sharapova faced a difficult test in her third round match, dropping the first set to German Sabine Lisicki. The Russian, who has won all four slams in a hugely successful career, eventually pulled off a 6-7(8), 6-4, 6-3 win.
Sharapova, who carried the Russian flag at the opening ceremony, will now face former world number one Kim Clijsters in the quarter finals after the Belgian ground out a 6-3, 6-4 win over Serbia's Ana Ivanovic.
Clijsters, who is retiring at the end of this season, hit less winners than her Serbian rival, but forced 41 errors from her..
"The conditions were not easy today but it was a fun court to play on. Most of the TV courts are huge and there's a lot of room around them but here you can really feel the impact of the crowd and it was very enjoyable," Clijsters said.
"I feel like I've been playing some really good tennis in the first three matches here, it's just a matter of trying to keep that up and before every match I need to refocus and stay on target.
"There was lots of Belgian support and Serbian too, it was fun."
Victoria Azarenka also progressed to the quarter finals after she comfortably beat Russian Nadia Petrova 7-6, 6-4. The world number one has enjoyed a comfortable route to the quarters, but now faces Venus Williams' conqueror Angelique Kerber.
Caroline Wozniacki completes the women's quarter final lineup. The Danish player looked to be rediscovering the form that made her number one in the rankings as she beat Slovakia's Daniela Hantuchova 6-4, 6-2.