At 32, the Australian is in the twilight of a career in which he achieved No.1 status as well as victory in the US Open in 2001 and Wimbledon the following year.
His best days may be behind him, but the battling spirit and instinct has far from wilted.
His epic second round, five-set win over the 2009 champion Juan Martin Del Potro on Friday night had the old romantics gushing at the return of "Rusty", the man who two years ago was told by six different doctors that he needed a reconstruction of the big toe on his left foot and should retire.
Today, the 21st-seeded Russian, Mikhail Youzhny, stands in the way of a first major quarter-final appearance since Wimbledon in 2009.
"This is what Lleyton Hewitt lives for," purred John McEnroe. "This is why he's going to be in the Hall of Fame. He's still showing us what he's got in the tank. It's a testament to the man. He's in my top top five of what I call effort players; the guys who fight more than anyone we've ever seen.
"I'd have Rafael Nadal, Jimmy Connors and Lleyton Hewitt, then Michael Chang and David Ferrer in that top five. It's incredible what Hewitt is doing. It was slipping way."
Youzhny, who saw off the 12th-seeded German veteran Tommy Haas 6-3, 6-2, 2-6, 6-3 , will provide as stern a test as anything which has gone before. Hewitt, typically, is up for the challenge. Almost having tennis ripped away from him has reawakened the beast.
"I thought my career was over when I had the last foot surgery. I don't know another athlete that's come back from it, "admitted the Australian. "So, yeah, as confident as my surgeon and I were with everything, and it went as well as possible, we didn't know until I actually tried running on it.
"Then it took a lot longer once I was able to come back on the tour, it took a lot longer to get any kind of confidence and play pain free again. There was definitely a time those first few tournaments that I came back from that last operation where, you know, if it was still hurting as much as it was then now, I wouldn't be playing still.
"It's always great to come back to where it all started for me. The atmosphere in New York suits my personality. It's a lot of fun here, always."