MELBOURNE • Roger Federer apologised yesterday after he sparked a row with Bernard Tomic by upbraiding the Australian about his work rate - without first checking his ranking.

The 17-time Grand Slam champion told Tomic he had to work harder if he wanted to reach the top 10. That prompted Tomic to point out that the Swiss great was also some way away from the level of top-ranked Novak Djokovic, who crushed Japan's Kei Nishikori 6-3, 6-2, 6-4 yesterday to set up a semi-final meeting with Federer tomorrow.

The Swiss admitted yesterday he had made the comment thinking that Tomic was still ranked at about 50th in the world. When he checked the rankings, he realised the 23-year-old had risen to 17th.

"I didn't know his ranking was as high as it was, to be honest. I thought he was like 50 or 60 and he was top 20," he said. "That was my bad. But I still believe it's a big difference, top 10 for a week or for a year or for multiple years, and getting there is not easy.

"It's a lot of dedication, hard work. There's a lot of guys who have the potential right now, not just him. That's why I think it got brought up in many ways."

He also warned wayward Australian Nick Kyrgios that the next two years are vital to realising the 20-year-old's huge potential on the tennis circuit after a recent rocky patch in his career.

"I think he's a great player. I think he's enjoyable to watch. I know some people might not like it. I like it. He's got a lot of personality," the Swiss great said.

"The advice I would give him, just that he's aware of the fact how important the next couple of years are. Otherwise the train leaves the station and you're maybe not on it.

"It would be a pity to waste talent and all that, even more so in this day and age because I feel talent brought you further, back in the day. Too many guys have talent. Too many guys are working hard."

AGENCE FRANCE-PRESSE