Rafael Nadal vs. Roger Federer: Preview for 2013 ATP World Tour Finals Clash

Roger Federer masterminded a calm comeback victory over Juan Martin del Potro on Saturday to set up an all-star semi-final encounter against Rafael Nadal on Sunday.

The 2013 ATP World Tour Finals have already thrown up a batch of meetings between the world's finest talents but are only set to see the competition get tighter as we head into the final four.

On paper, Nadal would look the favourite to book his place in the London final. The Spaniard has made his way to 16 semi-finals of the 18 singles tournaments he's featured in this season, while opponent Federer has managed to reach that stage on just eight occasions in 2013.

This pair in particular have a long and well-chronicled history playing against one another, making for a meeting between two of this generation's most iconic tennis figures at the O2 Arena. 

Head-to-Head Record

Nadal: 21 wins

Federer: 10 wins

After a disappointing 2013 season, Federer will be hoping that this weekend's clash against Nadal takes a different course than their most recent meetings. 

In 2013, the Swiss has met Nadal on three occasions and was defeated every time, losing in the quarter-finals of both the Indian Wells Open and Western Southern Open, as well as in the final of the Rome Masters.

What is worth mentioning, however, is that the Spaniard is yet to dispose of his very well-known opponent when playing on indoor hard court.

In these conditions, it's Federer who has reigned supreme over the years, triumphing on all four occasions that the pair have done battle.

With that in mind, Sunday could either be the day that Nadal again shows himself to be limited in one very specific area of his game or finally gets the better of his old foe indoors.

Form Guide (Last 5 Tournaments)

Nadal: One win, one final, two semi-finals

Federer: One final, one semi-final, one quarter-final 

On paper, Rafael Nadal comes into the penultimate London stage as firm favourite, having made at least the semi-finals of his last three tournaments.

Having said that, Federer has seen his form rise of late and recently made back-to-back finals for the first time this season—the ATP World Tour Finals being his third in a row.

Nadal is so far unbeaten in London this past week and topped David Ferrer, Tomas Berdych and Stanislas Wawrinka on his way to Sunday's meet, while Federer surrendered a loss to world No. 2 Novak Djokovic.

It's the Spanish representative who's coped better with this type of pressure in 2013, however, with Nadal managing to appear in 13 singles tournament finals, while Federer has crashed out at the semi-final stage on five of eight occasions this year.