(CNN) -- Roger Federer and Andy Murray took contrasting routes into the last 16 of the U.S. Open Saturday in 32-degree heat and stifling humidity.
Top seed Federer beat 25th seed Fernando Verdasco 6-3 6-4 6-4 to make the fourth round for the 12th successive year.
But Murray nearly fell victim to the conditions against his Spanish opponent Feliciano Lopez, surviving a grueling four-set encounter.
The third seed, who beat Federer to win the Olympic title last month, led by two tiebreak sets until wilting in the third.
Up a break, the Briton conceded the advantage and was broken himself three times as the big-hitting left hander Lopez took command.
Murray also struggled to hold in the fourth, but a gritty effort took him to the third tiebreak of the match, which he won 7-4 to progress after over three and a half hours.
He will next face the winner of a later match between American James Blake and 15th-seeded Canadian Milos Raonic.
"This was the first match I had played in this humidity for a while so it was tough," Murray admitted to reporters after his escape.
Meanwhile Federer was never seriously troubled as he earned a clash with either American 23rd seed Mardy Fish or Gilles Simon, the French 16th seed.
Spanish hopes in the absence of the injured Rafael Nadal now rest with consistent Nicolas Almagro, who beat American wildcard Jack Sock in four sets.
Croatian12th seed Marin Cilic beat Japanese 17th seed Kei Nishikori, also in four sets, to earn a last 16 match with unseeded Martin Klizan.
The Slovakian, who accounted for Jo-Wilfried Tsonga in the previous round, beat his doubles partner Jeremy Chardy of France 6-4 6-4 6-4.