US Open: Just what doctor ordered for Lleyton Hewitt as he beats former champion Juan Martin del Potro

Hewitt lives for the moment of winning - which is why he's never thrown in the towel (AFP)

It is 12 years since Lleyton Hewitt beat Pete Sampras to win the US Open but the 32-year-old Australian has never forgotten what it felt like. Hewitt lives for such moments, which is why he battles on, despite countless injury setbacks, always believing that he can recapture some of those magical moments on the biggest stages.

Hewitt rolled back the years with a sensational performance here in Arthur Ashe Stadium to beat Juan Martin del Potro 6-4, 5-7, 3-6, 7-6, 6-1. "I don't know how many years I have left in me so I was just hanging to get back on this court again," Hewitt said afterwards. "It was a hell of a lot of fun. I cherish every match I get. This is why I still play, to have moments like this."

Hewitt's latest comeback followed major foot surgery last year. Cartilage was removed from the big toe of his left foot, painful bone spurs were shaved off and a steel rod was inserted. Six different doctors had told him that he should retire.

Rafael Nadal took his record on hard courts this year to 18 wins from 18 when he beat Croatia's Ivan Dodig 6-4, 6-3, 6-3. Fellow Spaniard David Ferrer was the first man into the last 16 with a 6-4, 6-3, 4-6, 6-4 win over Kazakhstan's Mikhail Kukushkin.

Petra Kvitova ended a miserable year in Grand Slam tournaments when she was beaten 6-3, 6-0 by the world No 81 Alison Riske of the United States. The 2011 Wimbledon champion, who had been unwell 24 hours earlier, had her blood pressure taken during a time-out in the second set and had blood tests afterwards.

The Czech player had a similar problem at Wimbledon. "I think it's the same," she said. "I had a blood test to see if it was bacteria or virus, and it was a virus. I didn't have any sore throat or anything like that. I had just a very high fever. It's unlucky at a Grand Slam."