Roger Federer and Rafael Nadal will stage the last chapter of their battle to finish the year as world number one when the ATP Tour Finals get under way in London on Sunday.
Federer goes into the Tour Finals at the O2 Arena top of the world rankings, but the Wimbledon champion knows second placed Nadal can still snatch first place if the Spaniard wins the prestigious end-of-year event.
The race for pole position is the latest installment of an enthralling rivalry between two of the sport's all-time greats. Although Federer and Nadal remain friendly enough off the court, the Swiss star relishes his position as tennis's pre-eminent force and has no intention of surrendering it over the next week.
While Federer is setting his sights firmly on that number one position, Nadal is less concerned about the rankings.
The four-time French Open champion has endured the most traumatic year of his career, with his parents' seperation proving a significant distraction before injury denied him the chance to defend his Wimbledon title.
Now fully fit again Nadal, 23, claims he is just relieved to be able to test himself against the world's best again.
British number one Andy Murray and Juan Martin del Potro, who beat the Swiss in September's US Open final, are also in Federer's group.
Group B features Nadal, reigning Tour Finals champion Novak Djokovic, Nikolay Davydenko and Sweden's Robin Soderling, who was handed his place when Wimbledon finalist Andy Roddick pulled out through injury earlier this week.
London is staging the Finals for the first time in the event's 40-year history and, while Federer and Nadal can't meet before the semi-finals, the sell-out crowds in the English capital will see a host of other intriguing ties, starting with home favourite Murray's clash against US Open champion Del Potro in the event's opening match on Sunday.
Murray, 23, has long been regarded as a potential grand slam champion, but while the British number one is still to win his first major, Del Potro, 21, has already done just that, fighting back from two sets to one down to beat Roger Federer in New York.
Del Potro hardly eased the pressure on Murray when he admitted that he expected the Scot to be a grand slam champion by now.