Rafael Nadal hailed Lleyton Hewitt's fighting spirit on Saturday, but admitted it was hard to even think about still battling away on the tour when he reaches the Australian's age of 32.
Hewitt caused the biggest upset of the US Open in a Friday night thriller when he stunned 2009 champion and sixth seeded Argentine Juan Martin Del Potro in five sets.
It was the injury-cursed Hewitt's first win over a top 10 player in New York since the night he beat Pete Sampras to win the US Open in 2001.
"I was happy for Lleyton. He's a great fighter after a long time with a lot of injuries to have the chance to be back," said Nadal.
"To be still on the tour with motivation to keep playing, keep fighting is something that I admire a lot in him. It's great for a player like him to have a big victory like he had against a very tough opponent like Juan Martin."
Nadal can sympathize with Hewitt's injury travails.
The Australian was told to retire from the sport but opted to undergo a painful toe surgery where a metal plate was inserted in his foot in an effort to extend his career.
For his part, Nadal was sidelined for seven months until February this year as he battled an ongoing knee injury.
The Spaniard is five years younger than Hewitt and believes that with his own injury history, it would be impossible to say for certain that he will still be playing when he gets to his early 30s.
"I am 27. That's the only thing important today. Nobody knows what's going to happen tomorrow," said Nadal.
"I feel very lucky for all the things that went well in my career. I have the chance to decide when and where. So for the moment, I don't think about that, because my motivation is to keep playing for a long time.
"I don't know if three, four, five, six years. I go day by day. Important thing is be happy. I'm happy today."
On Saturday, Nadal eased into the US Open last 16 with a 6-4, 6-3, 6-3 victory over Croatia's Ivan Dodig, his only concerns being a shortage of towels and a worrying pass by a low-flying jet.
The second-seeded Nadal, a 12-time major winner and the 2010 champion in New York, hit 37 winners and faced just two break points and goes on to face Philipp Kohlschreiber, the 22nd seed from Germany, for a quarter-final spot.
Passage to the last eight could mean a first-ever US Open showdown against old rival Roger Federer.
"I started the match with a high intensity. I lost to Ivan the last time we played in Montreal and he won two hard matches here against Fernando Verdasco, a lefty like me, and Nikolay Davydenko," said Nadal.
"I think I played my best match of the week so far today."
Nadal, who has yet to drop serve in three rounds so far, admitted it was an emotional experience returning to New York after missing the 2012 tournament through injury.
"This court is very special. I have many unforgettable memories of this court so thank you for making me feel like I am at home," added the Spaniard, whose title in New York in 2010 allowed him to compelete the career Grand Slam.
The 27-year-old Nadal, who has collected nine titles since his return from a seven-month injury layoff in February, was never troubled by world number 38 Dodig, who beat the Spaniard the last time they met in Montreal in 2011.
His win took his year record to 56 victories against just three losses and extended his hardcourt run to 18-0.