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."
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).
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.
Rafael Nadal headlined the night matches, which were impacted by an unattended backpack left near the main gate.
Police stopped vehicle and foot traffic in the immediate area because of the bag. Authorities then found it did not present any safety risk.
Det. Roy Rutland of the Miami-Dade Police Department said personnel working at the tournament found the bag. Rutland says the department's bomb squad was responding "to mitigate the potential threat."
"There was a bomb threat and a lockdown but that's all I know about it," women's No. 1 seed Serena Williams said shortly after the situation ended. "Scary."
The investigation was announced during a match between Williams and Angelique Kerber, which proceeded as scheduled. Hundreds of people were trying to leave the facility after that match and were stopped at the gate before being allowed to eventually walk out of the tennis center.
Nadal and Fognini were warming up when police announced that the situation had been resolved.
Information from The Associated Press was used in this report.