In the second set of the fourth round encounter between Roger Federer and Tommy Robredo at this year’s US Open, Federer looked his age. His shoulders had drooped and his face gave away the look of a man who was at war with himself, searching for the genius that only a few years ago allowed him to dispatch a player like Robredo with consummate ease.

There’s always a sense of poignancy and tragedy when watching a great athlete going through the inevitable decline. As a fan, it makes you long for those moments of greatness, and wish that somehow he or she will be able to channel the magic that once existed.

Federer’s career has been something of a fairytale. His career for the most part, has encapsulated the physical concept of Entropy, or what is known as the Arrow of time. It's a concept that dictates that time can only travel in one direction: Forward.

From his days as a brash teenager from Basel, Switzerland, with bundles of sheer talent but bridled with anger issues, tantrums and broken rackets, Federer emerged as the cool, classy, artist with the perfect game — a game that has been described as ballet, as the embodiment of the European aesthetic; as lethal ferocity disguised as poetry in motion.

In 2006, the late writer David Foster Wallace likened watching Federer play tennis being akin to a religious experience in a piece that has become a part of tennis literature.

He wrote of what he called “Federer moments.” These are times, he wrote, “that as you watch the young Swiss play, when the jaw drops and eyes protrude and sounds are made that bring spouses in from other rooms to see if you’re OK.”

He made his entrance with the proverbial bang — an enthralling fourth round five-set win against the then King of Tennis Pete Sampras at tennis’s Mecca, The All England Club in Wimbledon.

That moment on Federer’s story arc had been nothing but a steep incline, amassing grand slam titles and shattering records like the mortal among us would collect stamps.

His aura acquired such a uniquely haloed status that on many occasions it seemed he had won a match before it was actually played. The actual match was merely an exhibition of the many ways he could strike a ball over the net. The word ‘doubt’ was never uttered in the same sentence as his name, other than when Rafael Nadal was in the picture.

Nadal was the classic counterpoint. Long haired and muscular with his Majorcan tan, he looks more like Mowgli the man-cub from the Kipling’s Jungle Book than the classic tennis player.

In the age of Federer, with the GQ looks and the cricketer’s cardigan and the all court game, Nadal provided the requisite contrast to men’s tennis.

In 2008, Federer was supposed to march into sports immortality. He stood at the precipice of history only three Grand Slams shy of breaking Pete Sampras’ record of 14. Going by the previous four years, another routine Federer season would have accomplished the feat.

But history as we know her is an elusive creature. She makes you cry and crawl and dishes out every obstacle in your way. And for Federer, as he stood at the edge of the cliff, his footing gave way.

The year didn’t start well. He was dispatched in the semis of the Australian Open, by a cocky young Serb named Novak Djokovic who’d been nipping at his heels the previous year. The “monster” that he had created had been subdued.

At the French Open that year, Nadal demolished Federer in a straight-set route that left some people aghast.

But there was hope still. Wimbledon was just around the corner. The cleansing green pastures that Federer had called home since he took over the deed to centre court in 2003 was just where he could restore order.

This was his house for five years, where he took the baton from Sampras and where he walked out to court jacket and all.

Many consider that Wimbledon final in 2008 as the greatest match in history. It was a gargantuan battle of wills, ripe with rain delays, failing light and history on the line. Tennis has never seen shot making and ball striking of the likes that was seen on that Sunday.

After a slow start and a welcome rain delay Federer found his game and raised it to a level that only Nadal could have pushed him to. The loss was a crushing blow to Federer.

Federer went on to win five grand slams since that pivotal match, including breaking Pete Sampras’ grand slam record of 14 and cementing his place as arguably the greatest player to hold a racket.

But it was that moment where opponents knew that the tide was turning.

It heralded the beginning of Federer’s second act. While the first act was about his impeccable technique and artistry as well as about his unprecedented reign at the top of men’s tennis, the second has been about his ability to take on younger and stronger adversaries in the form of Nadal, Djokovic and Andy Murray.

There is no doubt that Federer’s game, at the age of 32, is not where it once was. That immaculate forehand goes off one too many times. Break points are not converted. The belief that once existed, the faith in his own perfection has been weakened if not lost.

Over the course of Federer’s nearly decade long reign at the top, he figuratively and literally, re-embodied men’s tennis in a way no one had anticipated. At a time when power base-line tennis looked to be the future, he brought back elements that seemed to be on their way out.

“Subtlety, touch, and finesse are not dead in the power-baseline era. For it is, still, in 2006, very much the power-baseline era: Roger Federer is a first-rate, kick-ass power-baseliner,” Wallace wrote. “It’s just that that’s not all he is. There’s also his intelligence, his occult anticipation, his court sense, his ability to read and manipulate opponents, to mix spins and speeds, to misdirect and disguise, to use tactical foresight and peripheral vision and kinaesthetic range instead of just rote pace — all this has exposed the limits, and possibilities, of men’s tennis as it’s now played.”

While Nadal may have been Federer kryptonite in human form, even he realised that to win in the Federer era, his unimaginably physical game would not be enough to win on all surfaces.

Every generation, in most sports, an athlete comes along and changes the very game itself. Federer did with tennis, what Tiger Woods did for golf, what Michael Jordan did for basketball, and what Brian Lara did for cricket. They dominate the sport with such ease, leaving opponents wondering what more they could do.

But eventually, others catch up.

Nadal, Djokovic and Murray in this respect are in many ways creations of the Federer era. He set the bar of what it takes to win in tennis, but Djokovic and Murray have caught up and in some ways passed it.

This year, Federer saw some of his most impressive streaks ended. Losses to unheard of names like Daniel Brands (No. 55), Federico Delbonis (No. 114), and Sergiy Stakhovsky (No. 116) since Wimbledon are evidence of a player who’s lost some of the magic he once weaved.

The likelihood that Federer will win another slam is slimming, but it’s always dangerous ruling out the heart of a champion. Even during his unceremonious losses, the Swiss great has shown that he is still capable of producing “Federer moments”.

It’s now a time for savouring these moments, for they are surely not going to last.