Miami Master PHOTOS: Li finds Keys to victory; Federer sizzles

World No 2 Li Na finally made her first appearance at the Sony Open on Sunday, taming Madison Keys in an unsteady effort while three-time champion Venus Williams was also made to work under a blazing Florida sun for her spot in the fourth round.

Li displayed some signs of rust in her first match of the tournament after receiving an opening round bye and a walkover when Alisa Kleybanova withdrew from their second round meeting with illness.

She had to fight off three set points and an early break in the second set before clinching a 7-6 (7-3), 6-3 win over her American opponent.

Keys, who lives in nearby Boca Raton, had her Chinese opponent on the ropes several times but allowed the experienced Li to escape time-and-time again.

"She's No 2 in the world for a reason. She just won the Australian Open for a reason," said Keys. "She's a great player.

"I played well at times and she just played the bigger points really, really well.

"There is a lot to be happy with but there is also some stuff I need to work on."

Li got off to a strong start, grabbing the early break and a 3-1 lead, but the big hitting Keys answered with two breaks of her own, surging in front 5-3.

Keys however could not convert any of her three set points, Li wiggling free with a break and forcing the set to a tie-break which she easily won 7-3.

The American again had Li under pressure in the second, grabbing the early break to go up 2-0, but could not sustain the pressure as Li, having now hit her stride, stormed through the next five games on her way to victory.

"I think it was pretty tough match, she played well, big serve, big forehand, especially when she was 3-1 down and then come back 5-3 up and serve for the first set," said Li.

Williams, seeded 29th at the tournament she considers her home event, battled Casey Dellacqua for almost two and a half hours before subduing the determined Australian wild card 6-4, 5-7, 6-4.

Williams was not at her best against Dellacqua committing 44 unforced errors and six double faults but she did not lack for fight in the blistering mid-day sun.

"If I go down it's never easy," said Williams. "At least my opponent knows they have to go to the end of the earth to take me out no matter what the circumstances, usually.

"I do try and compete. I mean, being out here, even if it's not your best day, no matter what the circumstances are."

Third seed Agnieszka Radwanska of Poland continued to confirm she is over the knee problem that plagued her in the final in Indian Wells last Sunday, registering a 7-5, 6-3 victory over Russian Elena Vesnina.

In other third round action, Slovakia's Dominika Cibulkova, the 10th seed, was a 7-6 (8-6), 6-4 winner over Frenchwoman Alize Cornet.

Defending champion Andy Murray and 17-time Grand Slam winner Roger Federer sizzled under a Miami sun, speeding into the fourth round with convincing straight sets wins.

Federer, twice a winner on the Miami hardcourts, needed just 62 minutes on a sweltering centre court to dispose of Dutch qualifier Thiemo De Bakker 6-3, 6-3.

A resurgent Federer has shown that he is coming to grips with a new larger racquet, a change that the Swiss had resisted.

But Federer has seen improved results with the racquet, collecting his 78th career title in Dubai in February and reaching the final in Indian Wells to move back into the top five of the world rankings.

"I think it (the racquet) just gives me easier power, especially on the first serve," said Federer. "And I think as time now goes by, I'm getting a better feel for how is the ball going to react, you know, how much spin do I need to put on to stay really accurate and put it really close to the line.

"But then again this wasn't Andre Agassi on the other side, or Djokovic. It's just important for me to keep that up and remind myself it's going well so far."

Murray appeared to be adjusting just fine to life without coach Ivan Lendl, easing past Spain's Feliciano Lopez 6-4, 6-1.

After getting the defence of his Sony Open title off to a shaky start with a three-sets win over Matthew Ebden on Friday, Wimbledon champion Murray was more in command against Lopez improving his record to 9-0 against the Spaniard in just 73 minutes.

"It was obviously a more comfortable score line than the other day."

Murray has been in the Miami spotlight for more than his play this week after announcing he had ended his successful partnership with Lendl, who helped steer him to a pair of grand slam titles and an Olympic gold medal.

Lendl, who maintains a Florida residence, was in the stand catching some of the Sunday match, leading Murray to joke that the two men were renewing their partnership.

Seven of Murray's previous eight matches had gone three sets but the Briton, who has a Miami residence, made sure he would spend as little time as possible under a punishing sun, breaking Lopez three times in the second set, sweeping the last four games.

"It was really hot. I don't know how hot it was but when we came over at like 9:30 it was already 80 Fahrenheit (27 Celsius) and it was extremely humid," said Murray. "I have played a few matches here where it's been very, very hot but it doesn't always stay like this for a few days in a row in March.

"It's not easy conditions."

In other third round action, Frenchmen Richard Gasquet and Jo-Wilfried Tsonga advanced in contrasting fashion.

The ninth seeded Gasquet had easy passage beating 17th seeded South African Kevin Anderson 6-3, 6-4 while 11th seeded Tsonga rallied for a 4-6, 7-6(6), 7-5 win over Cypriot wildcard Marcos Baghdatis.

Spaniard Tommy Robredo, the 16th seed, advanced with a 6-3, 6-4 win over Frenchman Julien Benneteau.