(CNN) -- Fourth seed Andy Roddick limped out of the Shanghai Masters on Tuesday after being forced to concede his opening match against Stanislas Wawrinka due to a knee problem.
Andy Roddick's hopes of reaching the season-ending ATP World Tour Finals have dipped in recent weeks.
A day after complaining about the ATP Tour's grueling schedule, the American gave his Swiss opponent an unexpectedly easy ride into the third round when he hurt his left knee while leading 4-3 in the first set.
It was the second successive early exit for the world No. 6, who had a first-round bye, and could have some impact on his chances of qualifying for the season-ending ATP World Tour Finals in London at the end of next month.
The 27-year-old is hoping to secure one of the three remaining places for the eight-man tournament, with Roger Federer, Rafael Nadal, Novak Djokovic, Andy Murray and Juan Martin Del Potro having already qualified.
He has struggled since losing an epic Wimbledon final to Federer, going out in the third round at the U.S. Open and then crashing at the first hurdle in his China Open title defense.
The unseeded Wawrinka will next play 13th seed Radek Stepanek, with the Czech progressing after a 7-5 6-4 victory against German Andreas Beck.
In-form Russian Nikolay Davydenko kept his London hopes on the boil as he also reached the third round after beating compatriot Igor Kunitsyn for the second week in a row.
The sixth seed, who won the Malaysia Open and reached the quarterfinals of the China Open, triumphed 6-4 6-2 to set up a clash with Fernando Gonzalez.
The 10th-seeded Chilean crushed Brazilian qualifier Thomaz Bellucci 6-3 6-4 as he bids to reach the season finale for the third time.
In Tuesday's first-round matches, unseeded Czech Tomas Berdych upset 12th seed Marin Cilic 7-6 (10-8) 3-6 6-4, repeating his win over the Croatian in the Davis Cup semifinals last month.
Berdych's reward for defeating last weekend's losing China Open finalist is a clash with former world No. 1 Marat Safin, who is retiring at the end of this season.
Another former top-ranked player, Australia's Lleyton Hewitt, progressed after beating unseeded American John Isner 6-2 6-4 in the first match of the day.
He will next play 11th seed Gael Monfils following the Frenchman's 6-2 6-2 drubbing of compatriot Paul-Henri Mathieu.
French Open finalist Robin Soderling, also in contention for a place in the finals, cruised into the second round with a 6-3 6-4 win over unseeded Romanian Victor Hanescu.
The Swedish ninth seed will next play Nicolas Almagro after the Spaniard battled past Philipp Kohlschreiber of Germany in two hours and 11 minutes, winning 6-7 (2-7) 6-1 7-6 (8-6).
On Wednesday, top seed Nadal will open his campaign with a second-round match against American James Blake, while second seed Del Potro takes on unseeded Austrian Jurgen Melzer.