KEY BISCAYNE, Fla. -- Andy Murray heard a fan clamoring for a souvenir towel and tried to oblige by tossing one toward the courtside seats.
His throw fell way short.
That was about the only mistake Murray made Tuesday at the Sony Open.
Even with his surgically repaired back still nowhere near perfect, the defending champion continued his roll at Key Biscayne. He needed only 73 minutes to beat Jo-Wilfried Tsonga 6-4, 6-1 and set up a Wednesday quarterfinal with Novak Djokovic -- their first meeting since Murray won the Wimbledon final last summer.
"My game is getting there," said Murray, the No. 6 seed who acknowledged he was dealing with a sore back Tuesday. "The last six sets I've played, very high-level tennis, very few errors."
He'll need to keep it that way against Djokovic, who eased past Tommy Robredo 6-3, 7-5.
The second-seeded Djokovic even gave back a point in the second set. A groundstroke from Robredo clipped the baseline and Djokovic couldn't handle it, but the ball was erroneously called out. After a review showed the ball was in, the point was ordered to be replayed.
Djokovic shouted "It's OK, it's OK" as the fans applauded his sportsmanship.
"For me, it's something that is part of the sport, fair play," Djokovic said. "I expect everybody else to do the same. Of course, not everybody's the same, but for me, that's something that's normal. Just a normal, natural reaction."
Top-seeded Rafael Nadal topped 14th-seeded Fabio Fognini 6-2, 6-2. Nadal has dropped a total of nine games in six sets so far in this tournament.
Singles players with a combined 66 Grand Slam victories were in action Tuesday, including Roger Federer -- a winner of 17 of them himself. And he looked very much like the Federer of old, needing only 49 minutes to beat ninth-seeded Richard Gasquet 6-1, 6-2.
"Look, things went well out on the court today," Federer said, clearly understating matters.
Federer, the No. 5 seed, had 25 winners to Gasquet's eight, converted five of his six break chances and won 92 percent of his first-serve points in the second set. Next up for Federer on Wednesday night is 20th-seeded Kei Nishikori, who fought off four match points in the third-set tiebreaker and upset No. 4 David Ferrer 7-6 (7), 2-6, 7-6 (9) in a match that lasted just over 3 hours.
Ferrer had beaten Nishikori in the same round at Key Biscayne a year ago, their most recent meeting before Tuesday. No. 22 Alexandr Dolgopolov of the Ukraine also pulled off an upset, topping third-seeded Stanislas Wawrinka 6-4, 3-6, 6-1 to reach the quarterfinals. Another men's winner was Milos Raonic, the No. 12 seed who beat Benjamin Becker 6-3, 6-4.
The last American in the men's draw was ousted Tuesday night, when 10th-seeded John Isner lost to No. 7 seed Tomas Berdych 6-3, 7-5.
On the women's side, Maria Sharapova rallied from a break down in the first set to oust Petra Kvitova 7-5, 6-1 and earn a spot in the semifinals. She's been a finalist at Key Biscayne five times, but never the champion.
"I love the energy here," she said.
The fourth-seeded Sharapova, who needed three-setters to get through her two most recent matches at Key Biscayne, feasted on 30 unforced errors by the eighth-seeded Kvitova. Sharapova won 11 of the final 13 games and moved into a semifinal matchup with Serena Williams, the defending champion who won 62 of 100 points in her 6-2, 6-2 romp over fifth-seeded Angelique Kerber.
Williams broke Kerber twice in each set, faced only one break point and had a more than 2-to-1 advantage in winners. She's 15-2 all-time against Sharapova, winning the last 14 matchups, including the final at Key Biscayne last year.
"When you're playing champions, you like to play your best," Williams said. "She always gives me her best. ... I love playing her. I really do. It doesn't matter what surface. She's one of my favorite people to play."
Sharapova said she was eager to face Williams again.
"It's no secret that she's been a big challenge of mine, an opponent that obviously I would love to beat," Sharapova said.
Also, former No. 1 Martina Hingis teamed with Sabine Lisicki to reach the doubles quarterfinals. And foot and vehicle traffic outside the tennis center was briefly halted during the night session when a suspicious backpack was found near the main gate, but Miami-Dade police responded and quickly determined there was no threat.