Rafael Nadal of Spain celebrates defeating Alex Kuznetsov of the US during their men's singles match at the Australian Open tennis tournament in Melbourne, Jan 16, 2012. [Photo/Agencies]

Rafa Nadal eased into the second round of the Australian Open with a fuss-free 6-4 6-1 6-1 win over American Alex Kuznetsov on Monday but said he felt lucky to be on the court because of a big injury scare.

The world number two explained that he felt a "crack" on his right knee when sitting on a chair at his hotel on Sunday and needed physiotherapy that afternoon and all day Monday to recover in time for his match.

"Yesterday afternoon the most strange thing happened to me," he told reporters. "I stood up and felt the knee a little bit strangely.

"I moved the leg two times to try to find some feeling. After the second time there was unbelievable pain.

"I really couldn't move the knee ... I had no movement on the knee."

Nadal said scans did not show any major problem but added he was still in pain when he started the match with qualifier Kuznetsov.

"After the first 10 games ... I started to play normally," said the 25-year-old Spaniard. "I really don't understand what happened yesterday but I am really happy that today I was ready to play and I played a fantastic match."

Nadal, who came into the tournament with a lot of focus on his injured shoulder, played with his knee strapped and took 44 minutes to wrap up the first set.

The left-hander then ran away with the next two sets, dominating from the baseline and giving Kuznetsov just two break-point opportunities when he served for victory.

The injury scare which Nadal put down to a "pinched" tendon will also send shivers down the spines of the organisers who have lost the marquee player to injury in the quarter-finals of the past two tournaments at Melbourne Park.

Nadal suffered tendonitis in both knees for several months in 2009 and was forced to miss Wimbledon.

He will meet Tommy Haas in the second round after the German beat American qualifier Denis Kudla 7-6 3-6 6-0 7-5.