Rafael Nadal admitted Tuesday that he struggling to maintain focus as the end of a long and successful season draws near, with the world number one once again required to lift for the final leg of an Asian trifecta as top seed at the Shanghai Masters.

The winner of three of the four Grand Slams and a seventh title of the season at the weekend through a win over Gael Monfils at the Japan Open says that only the support of enthusiastic Asian crowds is seeing him through.

“The season is long, but I’m fine. I’m happy to be here and happy to be healthy,” said the top seed, who starts Wednesday in the second round after a bye against Stanislas Wawrinka of Switzerland.

“I’m more than happy with how the season has gone. But mentally, in this part of the season, it seems like is never going to end. But that’s our sport.

“Sometimes, the concentration to prepare the match is probably more than playing the match. But because the motivation, the feeling when you go on court, full stadiums, these things, everything is easier.” Nadal is counting the days until he can pause briefly at the end of the campaign, with his next event after Shanghai the Paris Bercy Masters from November 8 followed by the eight-man season finale in London.

“Now the last three tournaments remain. Sure, I’m more tired every day. But when you see the crowd supporting you, that gives you the power to keep working hard.” China’s Bai Yan, ranked 465th and playing in only the second ATP- level match of his career, will face Andy Murray in the second round after upsetting Czech Radek Stepanek 6-3, 6-4.

Bai, 21, recently won back-to-back Future events in China and has nothing to lose against two-time Grand Slam finalist Murray, whose game has slipped into a trough for much of the 2010 season.

“I’ll just do my best job and give my best performance,” said Bai.

“All I know is that I can probably put him under some pressure.

“Murray is much better than me, but I hope to learn from him in our match, and I think it will be a good opportunity for me.” Andy Roddick, fighting to return to his place in the ranking top ten after slipping to 11th this week, got started in less than an hour as German Philipp Kohlschreiber was unable to continue in a 6-3, 2-1 first-round loss. “But I thought I hit the ball well in what we did play today,” said the American. “I started to hit pretty well last week also, even though the match I lost to Gael (Monfils in Tokyo).

“I’m glad that I can get through today and keep trying to build on it.

“Obviously my first goal is finishing top eight (to qualify for the year-end championships next month in London). Hopefully doing that will take care of that one.” Wimbledon marathon man John Isner staged a comeback punctuated with 24 aces as the American spent two and three-quarter hours in overcoming Pole Lukasz Kubot 4-6, 7-6 (11-9), 7-6 (9-7).

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