With every passing U.S. Open there seems to be a rising tide of anxiety about the home nation' s fortunes that is starting to mimic what Britain has experienced at Wimbledon for so long.

So there was some relief on Monday night that the first player through to the men's last eight was a modestly-ranked American, Mardy Fish, who beat his third seed in succession when he upset France's Gael Monfils 7-5, 6-2, 6-2.

As Andy Murray prepared for his fourth round against Stanislas Wawrinka of Switzerland, the 35th-ranked Fish produced serve and volleying reminiscent of a bygone era when America was the sport's true powerhouse.

Magic Mardy: Fish clearly enjoys getting the better of Monfils and raising American spirits

That is no longer the case, as evidenced by the fact that the hosts were not unhappy that they at least managed to get three into the last 16 this fortnight. Andy Roddick is one of them, with the other being 20-year-old Sam Querrey.

In the women's game the picture is even more modest for the United States, with the two Williams sisters the only contenders among their tally of just four players inside the world's top 70.

Fish would be unlikely to have the class to upset Nadal in the quarter-finals, but he was way too good for the disappointing Monfils, who still struggles to fulfil his potential.

But as last year's beaten finalist and world No 3 Novak Djokovic discovered in his third round, there is no shortage of teenagers ready to go further than the 22-year-old Frenchman.

It took the Serb four hours to see off Croatia's Marin Cilic, one of a clutch of 19-year-olds who have emerged in the past 12 months to suggest that another wave of talent is on its way in men's tennis.

Roger Federer, Nadal and Djokovic, who eventually won in four sets, will surely be challenged by a generation likely to make the top 10 much stronger within two years than it is now.

The group coming up behind those in their early twenties - drawn from every corner of the world - features Cilic and two players facing each other last night for a place in the quarter-final against either Murray or Wawrinka, Kei Nishikori and Juan Martin del Potro.

Nishikori is set to be the best Japanese player ever in the men's game, a product of the Nick Bollettieri Academy in Florida, who has already won an ATP event this year.

Amazingly Del Potro, already ranked 17, has won four titles in succession while the tennis world has been looking the other way at the Olympics. When he took a week off prior to the Open, Cilic nipped in and won the tournament at New Haven.

Del Potro and Cilic are each 6ft 6in tall, while the last of the most promising quartet, Latvia's Ernests Gulbis, is 6ft 3in with as much natural talent as any of them.

Further down the line there is the hugely talented Wimbledon junior champion Grigor Dmitrov and the American Ryan Harrison who, before his 16th birthday this year, had already won a round of a main tour event.

'It's good to see these teenagers and rising stars,' said Djokovic, who maybe might not feel that way 18 months from now. 'Cilic, del Potro and Nishikori are all top 10 players in the future.'