Rafael Nadal beats Stanislas Wawrinka in Shanghai

Nadal has already secured his place in London's World Tour Finals

World number one Rafael Nadal beat Switzerland's Stanislas Wawrinka 6-4 6-4 to reach the third round of the Shanghai Masters.

The Spaniard was given a good workout by Wawrinka, ranked 21 in the world, but never looked in any danger.

Nadal will meet Jurgen Melzer next, after the Austrian overcame Spain's Daniel Gimeno-Taylor 6-3 7-6 (7-2).

Roger Federer breezed past John Isner 6-3 6-4 while Novak Djokovic eased to a 6-3 6-3 victory over Ivan Ljubicic.

"Playing against Wawrinka, it's impossible have an easy match," said Nadal after his win.

"He is a very good player and it was difficult to win in straight sets."

Despite taking a four-week break from the game, Federer looked sharp as he secured breaks in the fourth game of the first set and the seventh of the second to beat the big-serving Isner.

On his way to victory, the world number three produced a between-the-legs 'hot-dog' winner that is fast becoming a favourite technique.

He has previously deployed the shot successfully in the 2007 Dubai Open, and the 2009 and 2010 US Opens.

"It is the most consistent shot in tennis right now," joked Federer. "The last four I have tried have all come off. It is a little bit of fun for the fans, the players and the television."

Second seeded Djokovic, who defended the China Open in Beijing on Monday, wrapped up victory over Croatia's Ljubicic in 80 minutes.

Ljubicic, who upset Britain's Andy Murray on his way to the semi-finals in Beijing last week, proved far less of an obstacle to Djokovic who always had control of the contest.

Sweden's Robin Soderling progressed in straight sets as he overcame the serve of Janko Tipsarevic 6-3 7-6 (7-5).Tenth seed Andy Roddick retired hurt when leading 6-3 2-3 against Guillermo Garcia-Lopez of Spain.

The American strained his thigh as he attempted to change direction and, despite having the injury strapped, he conceded the match a game later.

"It was to the point where moving at all felt like I was getting stabbed in the leg," said Roddick.

Eighth seed Mikhail Youzhny was ousted by Germany's Florian Mayer 6-4 6-7 (5-7) 6-1 while Serbia's Marin Cilic, seeded 14th, went down 6-2 6-2 to Andreas Seppi of Italy.

Elsewhere, 11th seed David Ferrer progressed with a 7-6 (7-5) 6-3 win over Brazil's Thomasz Bellucci while 12th seed Jo-Wilfried Tsonga of France overcame Queen's winner Sam Querrey 7-6 (9-7) 6-1.

World number two Djokovic has taken a narrow 410-point lead over Federer in the world rankings after the Swiss took time out in the wake of his defeat by Djokovic in the US Open semi-finals in September.

The winner in Shanghai will earn 1,000 ranking points, although Federer missed the event in 2009 while Djokovic reached the semi-finals.

Richard Gasquet is up next for Djokovic after the Frenchman's 6-4 3-6 6-4 win over compatriot and 15th seed Gael Monfils, while Federer will face the winner of Seppi's clash with Taiwan's Yen-Hsun Lu.

Federer and Djokovic are scheduled to meet in the semi-finals

Djokovic is confident that a busy playing schedule will not catch up with him as the season nears an end.

"I'm playing well, moving well, motivated mentally and full of energy. I'm hoping that it's going to stay that way," said Djokovic.

"I didn't spend that much energy in Beijing. I won without dropping a set in the whole tournament."