New York: World No.3 Roger Federer survived his second scare in as many matches, but hung on to defeat Russian Mikhail Youzhny 6-1, 6-7(3), 4-6, 6-4, 6-2 to reach the third round of the US Open on Thursday.
Federer, who also claimed a come-from-behind five-set victory in his first round match against 19-year-old Frances Tiafoe, took advantage of a clearly hobbled Youzhny, who appeared to suffer from muscle cramps midway throughout.
Despite looking at times like he might retire from the match, Youzhny put in his best performance against the Swiss.
But the former top 10 player's fate was all but sealed when he double faulted to hand the Swiss a 4-2 lead in the fifth set and later saw Federer's record against him improve to 17-0.
The match marked the first time the 36-year-old third seed had ever started a grand slam tournament with back-to-back five set matches, raising questions about whether he has the stamina necessary to win his 20th career Grand Slam.
"These five set battles are actually a lot of fun," Federer said during an on court interview after the match.
"I feel quite warmed up now," he added with a laugh.
Despite the win Federer looked nothing like the dominant player who won the Australian Open to kick off the year and later cruised through Wimbledon without dropping a set.
He committed 68 unforced errors and the back injury that kept him out of the Cincinnati Masters earlier this month appeared to limit his mobility.
Next up for Federer is Feliciano Lopez, who defeated fellow Spaniard Fernando Verdasco in four sets in their second round match.