Defending champion Andy Murray survived a scare to reach the Olympic men's singles quarter-finals but Johanna Konta exited the women's singles.
Murray fought back after losing eight successive games to register a 6-1 2-6 6-3 victory over Italian Fabio Fognini.
He and Heather Watson then completed a 6-3 6-3 win over Spain's Carla Suarez Navarro and David Ferrer in the mixed doubles.
Murray will face American Steve Johnson in the singles last eight on Friday.
The Wimbledon champion was under pressure going into the third set before winning six games in a row to progress, in the process stretching his winning run to 15 matches following his French Open final defeat by Novak Djokovic in June.
"It was really, really hard out there and difficult to appreciate unless you were actually out there playing," Murray said.
"Sometimes the conditions don't allow for you to play really well and the conditions didn't allow that today."
It was a different matter in the doubles, where he and Watson competed a speedy victory after they received a late call-up when Romanians Monica Niculescu and Florin Mergea withdrew from the competition.
Watson, who was knocked out of the second round of the women's singles, admitted she "had her bags packed" before hearing she was playing.
"I genuinely had all my stuff packed, I had no idea, wasn't sure if we'd get in and then just got told, 'Get your kit on, you're on'," she said.
"I really do enjoy mixed doubles I enjoy the variety and trying to return the guy's serves, all of it."
Konta loses twice in one day
It was a frustrating day for British number one Konta, who delivered an error-strewn performance against Germany's Angelique Kerber.
Number two seed Kerber took just over an hour to beat Konta 6-1 6-2.
The Briton and mixed doubles partner Jamie Murray put in a strong performance against Americans Jack Sock and Bethanie Mattek-Sands, but Konta suffered her second defeat of the day as they were beaten 6-4 6-3.
Nadal and Del Potro progress
World number five Rafael Nadal maintained his bid to regain the Olympic men's singles crown he won at Beijing 2008 with a 7-6 (7-5) 6-3 victory over Frenchman Gilles Simon.
The 14-time Grand Slam winner, 30, had not played since the French Open in May and later withdrew from the mixed doubles with partner Garbine Muguruza.
He will, however, compete for gold in Friday's men's doubles match with Marc Lopez.
Meanwhile, Argentine Juan Martin del Potro, who knocked out world number one Novak Djokovic in the first round, is into the last eight after a 6-7 (4-7) 6-1 6-2 win over Japan's Taro Daniel.
"This has been a great tournament, a great week for me already," Del Potro, the 2009 US Open champion, said.
"I'm looking forward to go far, trying to fight for one medal. I'm still playing well, but the next round is going to be a really difficult match for me."
Del Potro will play Spain's Roberto Bautista-Agut next, while Nadal faces Brazilian Thomaz Bellucci.
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