Roger Federer vs. Rafael Nadal: The Swiss Will Win ATP Finals Semi

Few sportspeople possess as strong a claim to being artists as Roger Federer, and while the Swiss' peak years may now be behind him, he can still on occasion call upon his timeless mastery of the court to rise to the pinnacle of tennis.

The six-time ATP World Tour Finals champion was able to rally against Juan Martin del Potro, coming back from a first-set defeat to win 4-6, 7-6 (2) and 7-5 and set up yet another epic clash with Rafael Nadal.

They have arguably the greatest rivalry in the history of tennis, at least in terms of the two players' individual ability. Their impending semifinal match at London's O2 Arena should prove to be another titanic contest befitting of their canon of legendary showdowns from the past decade.

Having first faced each other in the third round of the Miami Masters in 2004, they contested every French Open and Wimbledon final between 2006 and 2008. The last of their championship battles at the All England Club is still widely considered to be the finest match ever played.

Nadal leads Federer in their head-to-head record with 21 wins to 10, but the Swiss holds the lead when it comes to both indoor courts and ATP Finals, where he has four victories out of four against the Spaniard.

That historical dominance on this surface will hearten the former world No. 1, who will see his latest matchup with Nadal as an opportunity to end what has been a disappointing season on a resurgent high note.

He'll make it 5-0 against Nadal on this surface. 

In his 32nd match against the Spaniard, however, he must disrupt the form of their more recent meetings. Nadal has won their last three games by rather handsome margins.

Fortunately, Federer has always changed tact in response to his aging decline. He has an almost Rocky Balboa-esque grittiness to compensate for his diminished agility of feet and mind.

No longer an effortless showman, he has become a scowling vision of severe concentration and at times frustration—as if disciplining himself for every percentage and margin lost due to error or sloppiness.

As reported by Sports Illustrated's Courtney Nguyen, Federer spoke of his reaction to dropping a shot against Del Potro in the second set: "How I could just play a loose game? Why is this happening? I'm trying to focus so hard for it not to happen."

Yet his victory over the Argentinian exemplified the veteran's ability to utilise his ferocious force of will even when his consistency fails him.

Unlike the big-hitting fictional boxer famously portrayed by Sylvester Stallone, Federer remains most comfortable close to the net, where his skill and imagination can still offer him a competitive advantage.

He may need the Italian Stallion's determined staying power to topple the current world No. 1, however. Their latest meeting is set to be a fitting spectacle akin to a heavyweight clash.

"This is going to feel like a final. Something to look forward to," he told the press in regard to the semifinal draw, as reported by Kevin Mitchell of The Guardian. "I don't have a day off and I'm just going to have to back up. I will try to make his life a bit difficult, and we'll see what happens."

Nadal has looked good so far at the ATP World Tour Finals, but he isn't infallible at present. On one of the Spaniard's least favourite courts, Federer will land a sucker punch to end his year in style.