US Open champion Roger Federer has challenged Novak Djokovic to join him and Rafael Nadal in the chase for grand slams.

World number one Federer saw off the rising Serbian star in straight sets in New York last night to claim a fourth consecutive US Open men's singles title, his 12th grand slam victory.

The only person to slow his charge towards Pete Sampras's all-time record of 14 major titles has been world number two Nadal, whose dominance on clay at the French Open has given the Swiss star his only genuine rivalry in tennis.

Djokovic, the 20-year-old from Belgrade, though, reached the semi-finals at Roland Garros and Wimbledon this year, losing to Nadal in both. He then beat Andy Roddick, Nadal and Federer in successive rounds on hard courts in August to win the ATP Masters Series in Montreal and followed that up by reaching his first grand slam final at Flushing Meadows.

Now the four-time US Open champion is expecting to see a lot more of the young pretender in years to come.

''I've enjoyed the young guys challenging me,'' Federer said. ''This is probably my biggest motivation out there.

''Seeing them challenge me, beating them in the final, it's really for me the best feeling, to be honest. If a rivalry comes along, great. So far we haven't played many times in finals of tournaments. It's always been quarter-finals, last 16.

''Now we've had two finals back to back, that always helps the rivalry, but I still obviously consider the one I have with Nadal much more serious at the moment.''

Djokovic, who forced the Swiss star to save seven set points and took him to two tiebreaks, could change that, Federer believes. Asked if the Serbian was good enough to step up to the next level, he said: ''Yes, he's been very consistent.

''I think if I would have played him twice in the semis of the French and Wimbledon then I would have had maybe more of a rivalry with him, but he landed on Rafa's side of the draw.

''So they've kind of got it going on at the moment actually.''