Maria Sharapova gained revenge for her Wimbledon fourth-round exit as she defeated Germany's Sabine Lisicki in a tight tussle to reach the quarter-finals of the women's singles at the Olympics.
The Russian was one of the favourites to win Wimbledon having completed her set of grand slam titles at the French Open to retake the world number one spot.
But Lisicki proved too strong and Sharapova came into this tournament ranked only third after seeing Victoria Azarenka and Agnieszka Radwanska overtake her.
The match looked set to go the same way when Lisicki edged a nip-and-tuck tie-break and then went a break up in the second set, but Sharapova showed her trademark battling qualities to turn things around and come through 6-7 (8/10) 6-4 6-3 after two hours and 47 minutes.
The Russian said: "I was really happy I was able to beat her today. Obviously losing to her a few weeks ago, I was not really happy with the way that I played, so I wanted to change that result.
"Even though I didn't play my best tennis, I was really happy that I got through it and I stepped up when I had to."
In the last eight, Sharapova will play Kim Clijsters, who kept alive her hopes of a medal at her first and last Olympics by defeating 11th seed Ana Ivanovic of Serbia 6-3 6-4.
Sharapova said: "There's no secrets going into the match tomorrow. We've been on the tour for many years, we've faced each other many times before, so we know each other's games.
"It's our first meeting on grass but she's such a tough competitor, such a great mover. She has so many great qualities as a tennis champion. It's always nice to play her, especially at this stage of an event like the Olympics."
It was the end of the singles road, though, for Venus Williams, who was edged out in two tie-breaks by German seventh seed and Wimbledon semi-finalist Angelique Kerber, going down 7-6 (7/5) 7-6 (7/5).
The 32-year-old still has the chance of a record fourth Olympic gold medal in the women's doubles with sister Serena, but she admitted a lack of matches caught up with her.
Venus has been battling Sjogren's Syndrome and is continually asked about retirement, but she is not ruling out another Olympic campaign in Rio de Janeiro in 2016.
The American said: "I haven't played a lot of matches this year and I haven't played a lot of singles the last couple of months.
"It would have been helpful for me to play some more matches for sure, to be in those situations more often. It's the points here and there that make the difference. Hopefully there's 2016 for me."
The most emphatic performance of the day came in the first match on Centre Court, where Serena Williams needed only 51 minutes to brush aside Beijing bronze medallist Vera Zvonareva 6-1 6-0.
Williams gave much of the credit to the roof, saying: "This is like a dream court. Grass is a dream court, but then to play indoors on grass... oh my god it's crazy."
The Wimbledon champion could not be happier with her form, adding: "I think I played better today and even in my second round than any match I played at Wimbledon. Today I was just playing unbelievable.
"I was nervous going into the match. I didn't speak to anyone. I had a bad practice. I was thinking, 'Gosh, I'm stressed out'. I had no idea I would play like this."
The fourth seed has been inspired by watching the achievements of her American team-mates in other sports, particularly swimming and gymnastics.
Williams said: "I think the women's gymnastics last night was ridiculously incredible for USA.
Everyone did so amazing. I had chill bumps, water and tears in my eyes. I was just so happy.
"Then seeing Michael Phelps get the 19th medal. I'm really good friends with Ryan Lochte. I'm texting him congrats, congrats, every day. All that inspires me.
"It's like we're here as a team. Even though we're over here and they're over there, we're all playing for the same country. It couldn't feel better."
In the last eight, Williams will play eighth seed Caroline Wozniacki, who was cheered on by the Danish handball team in a 6-4 6-2 victory over Daniela Hantuchova.
World number one Azarenka will take on Kerber after fighting off a determined challenge from Russia's Nadia Petrova, the Belarusian coming through 7-6 (8/6) 6-4.
The other quarter-final will see sixth seed and former Wimbledon champion Petra Kvitova face Russia's Maria Kirilenko.
Kvitova was particularly impressive, defeating Flavia Pennetta of Italy 6-3 6-0, while 14th seed Kirilenko defeated Germany's Julia Goerges 7-6 (7/5) 6-3.