Former British number one Greg Rusedski has urged compatriot Andy Murray to win quicker if he is to stand any chance of securing a second US Open title.
World number three Murray came from two-sets-to-love down to beat Adrian Mannarino 5-7 4-6 6-1 6-3 6-1 at Flushing Meadows on Thursday.
Murray battled illness and sweltering conditions as he advanced to the third round in New York after three hours and 17 minutes on Arthur Ashe Stadium.
The 2012 US Open champion has spent a combined total of six hours on court at the grand slam event across nine sets and Rusedski believes long matches are hurting Murray’s hopes of a third major title.
“It’s possible it could become a problem, because you don’t want to expend too much energy,” Rusedski told Sky Sports.
“You can lose a grand slam in the first week.
“He’s got a tough section because, if you look at it, it could be Stan Wawrinka, then Roger Federer, then Novak Djokovic in the final so he’ll want to be efficient.”
Next up for Murray, who boasts a 58-9 win-loss record this year, is Brazilian 30th seed Thomaz Bellucci.
“He’s got a rough section,” Rusedski added. “Bellucci played very well against [James] Ward, winning in straight sets, and has only played six sets while Murray has played nine.
“Bellucci is really dangerous, he leads their head-to-head 1-0. That was in 2011 in Madrid when they played at altitude and the ball was flying everywhere.
“He’s a big, strong striker of the ball but doesn’t move as well. It should be one that Murray gets through, but not easily.
“Murray will hope for an evening match in Saturday so the conditions aren’t as bad – I see him winning that in four sets.”