Garbine Muguruza's post-French Open slump continued Tuesday when she crashed out of the Olympics while Andy Murray and Rafael Nadal made the third round, happy to avoid Novak Djokovic's fate.

Third seed Muguruza slipped to a worrying 6-1, 6-1 loss to Monica Puig of Puerto Rico, the world number 34.

Puig, 22, closed in on what would be only Puerto Rico's ninth Olympic medal. The world number 34 will face Germany's Laura Siegemund for a semi-final spot.

Muguruza refused to admit that she has found it tough to adjust to being a Grand Slam champion for the first time.

Her results since the French Open in June tell a different story.

Before arrving in Rio, she lost in the first round at Mallorca and Montreal and made just the second round at Wimbledon.

"I didn't find a way to beat her but I am over it. I have to go on the court for doubles. I hope to keep going in that and the mixed (with Nadal) so I am not left with this bad taste," said the Spaniard.

Puig has had a breakout season, starting the year at 92 and now standing on the cusp of the top 30.

"I still have goosebumps," said Puig who collapsed to the ground in celebration after sealing victory.

"You keep it all bottled up. It's like a Coca-Cola bottle. If you shake it and shake it and shake it, it's going to explode.

"So I tried not to let it explode until the right moment."

Murray raced into the last 16, blitzing Juan Monaco of Argentina 6-3, 6-1.

Nadal was equally ruthless, claiming a seventh win in eight clashes against Italy's Andreas Seppi 6-3, 6-3.

Del Potro praise

Both men insisted they were happy not to have joined world number one Djokovic at the Rio exit door after the top seed was toppled by Juan Martin del Potro.

"Del Potro is a great player when he's fit, but he hasn't been fit very often in the last few years," said Murray, bidding to become the first man to win two Olympic singles gold medals.

"Juan Martin was playing really well. It was tough on Novak."

Murray will face France's Benoit Paire, the 16th seed, or newly-wed Fabio Fognini of Italy for a quarter-final spot. Nadal faces France's Gilles Simon.

"When the best player in the world loses, it's always a surprise," said Nadal as he reflected on Djokovic's exit.

"His success is diffcult to repeat. It's normal to lose some matches but he had a very negative draw against Juan Martin."

The 30-year-old Nadal is still in the men's doubles with Marc Lopez and will for the first time in his career play mixed starting Wednesday.

American seventh seed Madison Keys hailed Serena Williams for inspiring her to reach the quarter-finals.

Keys, 21, was the first woman into the last eight thanks to a 6-3, 3-6, 6-3 win over gritty Spaniard, Carla Suarez Navarro.

But she gave credit to 22-time Slam winner Williams, the top seed in Rio and defending Olympic champion.

"Hey, I'm happy to be on the same team as Serena Williams, it's thanks to her that I was able to get my ranking up and qualify," said Keys.

Keys will face promising Russian Daria Kasatkina for a place in the last four.

Two-time Wimbledon winner Petra Kvitova needed three sets to beat Russia's Ekaterina Makarova 4-6, 6-4, 6-4.

Britain's Johanna Konta required more than three hours to down former French and US Open champion Svetlana Kuznetsova 3-6, 7-5, 7-5.

Later Tuesday, Williams will continue her assault on a fifth career gold when she faces Elina Svitolina of Ukraine.

The 34-year-old American has won all four meetings against Svitolina, including at this year's French Open where she gave up just two games.

Second seed Angelique Kerber faces Australia's 2011 US Open winner Samantha Stosur.