Finally, the historic rivalry between tennis stars Roger Federer and Rafael Nadal is set to sizzle rather than fizzle. Federer, the Swiss world no. 1, closed out his semi-final against Spain’s David Ferrer 7-5, 3-6, 6-3 Saturday night in Madrid. Earlier in the day, Nadal, Spain’s world no. 3, dispatched his countryman Nicolas Almagro 4-6, 6-2, 6-2.

Sunday’s final at the Madrid Open will be remarkable for the fact that the two men have not played each other in exactly a year – when Federer defeated his longtime rival in the final of this very tournament. Having previously overtaken Federer’s no. 1 spot in 2008 after beating him in the finals of Roland Garros, Wimbledon, and the Australian Open, Nadal then endured a frustrating and uneven 2009, which saw him drop in the rankings and suffer several straight-set thrashings. However, few doubt that on form the two-headed, racket-wielding monster known to tennis junkies as “Fedal” remains the summit of the sport.

The match will be played on clay in Madrid’s postmodern arena known as the “Magic Box,” which features much metal along with semi-transparent poly-bicarbonate walls. The ball girls are models, the acoustics are horrendous, and the audience consists largely of the very rich, the very famous, the very beautiful, and stars from the Real Madrid soccer team.

Federer entered last year’s Madrid final having lost to Nadal five times in a row, and for many the rivalry seemed effectively over. To widespread surprise, Federer won the match 6-4, 6-4, not only conquering his nemesis in his home country but also on his beloved clay, a surface on which the Spaniard is considered virtually unbeatable. He then went on to Paris to win clay’s biggest prize of all, Roland Garros, after Nadal’s defensive game had been rudely disassembled in the quarter-finals by a giant figure out of a nasty Norse saga: Sweden’s Robin Söderling.

Since then almost everything has gone to plan for the Swiss. He outlasted American Andy Roddick in last summer’s epic Wimbledon final, narrowly lost the U.S. Open final to Argentina’s 6’ 7’’ Juan Martin del Potro, and then in January of this year won the Australian Open by outfoxing Scotland’s cerebral shot-maker Andy Murray, who had overcome Nadal in the semis. “He’s back, the Emperor, the King!” roared the on-court announcer as Federer stepped up to receive his trophy. Given that it was his 16^th victory in a Grand Slam final, two ahead of the previous record-holder Pete Sampras, one could forgive the hyperbole.

But a funny thing happened on the road from Melbourne to Madrid: Federer lost his form (or as he would say, his “rhythm”), and with it his confidence. In the meantime, Nadal has quickly reinforced his. We are now deep into the clay court season, Nadal’s preferred time of year, and he has already won the Monte Carlo Masters and the Italian Open, looking almost as indomitable as ever. Federer is routinely praised for his balletic style, but the way Nadal’s defensive prowess can drive even the best attacking players to despair constitutes a sui-generis athletic ballet in itself. Just in time, Federer is looking approximately like himself again, but on clay Nadal will always be the favorite.

Last season Federer also entered the Madrid Open in the midst of a slump. Victory turned his year around, while Nadal failed to win another tournament until last month – an almost year-long drought. Much of this was due to injury, along with the psychological fall-out from his parents’ divorce, but there is no doubt that almost every time these two men play each other a dramatic shift in the balance of power can occur.

So what is at stake this time? Nadal will be keen to reassert his head-to-head supremacy over his rival – always something of a statistical embarrassment since the Swiss has often been acclaimed as “the greatest player of all time” – and to do so in Spain’s capital. Both men will want to gain the psychological advantage going into the French Open, which Nadal has won four times, beating Federer in the final on three of those occasions. Yes, Federer won it last year, but – thanks to Söderling – without having to face Nadal. Such good fortune is unlikely to recur, but a victory on Sunday would nonetheless give Federer, who is not a true clay court specialist, a mighty boost of confidence.

For fans watching on TV (it is being broadcast live on the Tennis Channel at 12:30 p.m., with a repeat at 4 p.m.) one can only hope the match lives up to the hype, not always the case. If Nadal wins, he will surpass Andre Agassi’s record of 17 ATP Masters Series victories. If Federer triumphs, he will draw even with Agassi and Nadal. As always when these great players collide, tension abounds and records wait to be broken. The most important thing, however, will be the state of mind of each player as he exits the court. Roland Garros begins in a week.

Mr. Bernhard is a frequent contributor to The New York Sun.