Andy Murray (AP)
Rio de Janeiro - Defending champion Andy Murray raced into the Olympic Games last 16 on Tuesday, blitzing Juan Monaco of Argentina 6-3, 6-1, before sympathising with long-time rival Novak Djokovic over his stunning exit.
World number two Murray is looking to become the first man to win two Olympic singles golds, a cause helped when Juan Martin del Potro put out world number one Djokovic in the first round.
"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.
"In a 64-player draw with 16 seeds that's the kind of thing that can happen and 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.
Wimbledon champion Murray was hardly troubled by Monaco on centre court, extending a head-to-head winning streak which stretches back six years.
The Argentine never fully recovered from a fall in the second game of the opening set where he aggravated a long-standing hip injury.
Murray reeled off five games against the world number 108 and was soon 4-0 up in the second set before going on to claim victory in just 69 minutes.
"It felt good, I played well from the back of the court. There weren't many unforced errors," said Murray, 29, after racking up a 14th successive win since losing the French Open final to Djokovic in June.
Meanwhile 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, who made the Australian Open semi-finals in January, will face either Italy's Sara Errani or promising Russian Daria Kasatkina for a place in the last four.
Spanish seventh seed David Ferrer was knocked out by Russia's Evgeny Donskoy 3-6, 7-6 (7/1), 7-5.
Ferrer is the third top-10 seed to fail to make the third round after Djokovic and Jo-Wilfried Tsonga.
Two-time Wimbledon winner Petra Kvitova needed three sets to beat Russia's Ekaterina Makarova 4-6, 6-4, 6-4.
Later Tuesday, 2008 champion Rafael Nadal will play his fourth and fifth matches in three days.
First, the third-seeded Spaniard takes on Italy's Andreas Seppi, boasting a 6-1 career lead.
Then, he will team up with Marc Lopez to face Oliver Marach and Alexander Peya for a place in the men's doubles semi-finals.
Despite having not played a tournament for two months because of a wrist injury, the 30-year-old Nadal is piling on the workload in Rio.
He's also signed up for mixed doubles with Garbine Muguruza and they start their campaign on Wednesday.
Williams will continue her assault on a fifth career Olympic 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 while third-seeded Muguruza takes on Monica Puig of Puerto Rico.