* Top seed Nadal through to second round
* Injured Tomic quits after first set (Adds Tomic quotes)
By Ian Ransom
MELBOURNE, Jan 14 (Reuters) - Bernard Tomic was jeered by the crowd at his home Australian Open when he retired hurt after losing the opening set of his first round match against world number one Rafa Nadal on Tuesday.
Tomic, who has been criticised in the past for "tanking" - or deliberately not playing to his full ability during matches - had appeared uncomfortable from the outset under the lights at Rod Laver Arena, and took a medical time-out at the change of ends when leading 2-1.
The 21-year-old later ripped a bandage off his high left thigh at the urging off his camp and played out the set restricted and grimacing after points.
With the set lost at 6-4, 57th-ranked Tomic returned to his chair and shook his head at medical staff. After walking over to Nadal to tell him he would no longer go on, sections of the crowd booed, underlining local fans' frustration with a talent long criticised for lacking wholehearted commitment.
"It was sad. It's unfortunate. This opportunity I had to play against Rafa was huge for me," Tomic told reporters.
"Unfortunately, I couldn't compete. It was very difficult for me to say sorry to the crowd. I don't think they quite knew what was wrong with me.
"After, when he got that break (at 4-4), he was serving for the set, hit one ball, and I felt it even more. I thought, 'Am I really going to do this, spend a few more hours on court hurting my body?'
"I feel sorry because the crowd came and it was difficult for me. I did what's best for me. The crowd have to understand that."
Top seed Nadal, who will play 17-year-old Australian wildcard Thanasi Kokkinakis in the second round, had sympathy for Tomic, who was kicked off Australia's Davis Cup team in 2012 for attitude problems.
The Spaniard retired hurt during the 2010 quarter-finals when two sets down against Briton Andy Murray.
"I felt really sorry for Bernard. I was in that situation a few years ago and I know how tough is to take that decision," Nadal told reporters.
"But if you feel bad, there is no reason why you have to continue. You put in risk the next tournaments for nothing."
Spaniard Nadal, the 2009 winner at Melbourne Park, missed last year's tournament with a stomach flu which delayed his comeback from a knee injury, but could take little from his opening match barring the fact that he conserved energy on a stifling evening.
"Days like today, tomorrow that will be very hot, it's better to save little bit of energy," he said. (Editing by Patrick Johnston and Justin Palmer)