<p>Soderling, only competing in the elite year-end showpiece at London's O2 Arena because of the withdrawal of Andy Roddick, backed up his opening Group B victory over Rafael Nadal with another magnificent display to all but seal a semifinal spot. Djokovic looked disgruntled throughout the one hour 34 minute contest and offered resistance after losing the first set. <br /><br />Soderling, this year's French Open runner-up, had never beaten Djokovic in five previous clashes with the Serb and punched the air with delight after his opponent netted a lame volley on match point. <br /><br />Djokovic, the defending champion after winning the year-ender in Shanghai last year, will need to re-group quickly for his final round-robin match against Nadal on Friday.Nadal plays his second round-robin match later on Wednesday against Davydenko with both players seeking a first victory.<br /><br />On Tuesday, Federer did not have to be at his magical best but after a wobbly start he took control midway through the match and treated the 17,500 capacity crowd to some shots that only he can play, reeling off the last six games for a 3-6, 6-3, 6-1 victory. His second three-set win in Group A meant that world number two Rafael Nadal can no longer close the points gap in the rankings and Federer will have the honour of finishing the year as the world number one for the fifth time in his career. Only Pete Sampras, who managed the feat six times in the 1990s, and Jimmy Connors, who did it five times in the 70s, have achieved that since rankings were introduced in 1973. <br /><br />Federer also becomes the only man other than Ivan Lendl in 1989 to regain the year-end crown after being toppled from the summit by Nadal last year. <br />“After having a rough 2008, coming back this year and being able to dominate and play at the top when the depth in tennis is so great at the moment. I think it's a wonderful achievement," Federer told reporters. <br /><br />While Federer is untouchable in the rankings, the intricacies of tournament's unique format mean that his place in the semi-finals here is not yet guaranteed after Juan Martin del Potro's earlier victory over Fernando Verdasco meant that all four players in Group A can still progress. Federer tops the table with two wins but defeat by Del Potro, the man who stopped him in his tracks in the US Open final, on Thursday and victory for Murray against Verdasco would mean calculators are needed to work out the final standings.</p>
<p>Soderling, only competing in the elite year-end showpiece at London's O2 Arena because of the withdrawal of Andy Roddick, backed up his opening Group B victory over Rafael Nadal with another magnificent display to all but seal a semifinal spot. Djokovic looked disgruntled throughout the one hour 34 minute contest and offered resistance after losing the first set. <br /><br />Soderling, this year's French Open runner-up, had never beaten Djokovic in five previous clashes with the Serb and punched the air with delight after his opponent netted a lame volley on match point. <br /><br />Djokovic, the defending champion after winning the year-ender in Shanghai last year, will need to re-group quickly for his final round-robin match against Nadal on Friday.Nadal plays his second round-robin match later on Wednesday against Davydenko with both players seeking a first victory.<br /><br />On Tuesday, Federer did not have to be at his magical best but after a wobbly start he took control midway through the match and treated the 17,500 capacity crowd to some shots that only he can play, reeling off the last six games for a 3-6, 6-3, 6-1 victory. His second three-set win in Group A meant that world number two Rafael Nadal can no longer close the points gap in the rankings and Federer will have the honour of finishing the year as the world number one for the fifth time in his career. Only Pete Sampras, who managed the feat six times in the 1990s, and Jimmy Connors, who did it five times in the 70s, have achieved that since rankings were introduced in 1973. <br /><br />Federer also becomes the only man other than Ivan Lendl in 1989 to regain the year-end crown after being toppled from the summit by Nadal last year. <br />“After having a rough 2008, coming back this year and being able to dominate and play at the top when the depth in tennis is so great at the moment. I think it's a wonderful achievement," Federer told reporters. <br /><br />While Federer is untouchable in the rankings, the intricacies of tournament's unique format mean that his place in the semi-finals here is not yet guaranteed after Juan Martin del Potro's earlier victory over Fernando Verdasco meant that all four players in Group A can still progress. Federer tops the table with two wins but defeat by Del Potro, the man who stopped him in his tracks in the US Open final, on Thursday and victory for Murray against Verdasco would mean calculators are needed to work out the final standings.</p>