Roger Federer rarely suffers defeat and Saturday's loss to Rafael Nadal in the final of the Dubai Open would have left a bitter taste in the Swiss world number one's mouth.
Nadal's 2-6, 6-4, 6-4 victory snapped Federer's Open-era record of 56 straight victories on hardcourts and confirmed the Spaniard as a serious challenger to his world domination, as if we needed reminding.
Even for Federer, despite a chastening third defeat in four meetings with Nadal, it could well prove a positive experience and spur him to even greater feats.
A trawl through the last 30 years of men's tennis throws up some memorable rivalries.
Ice cool Swede Bjorn Borg scaled the heights to take on the raging John McEnroe, while the American firebrand regularly crossed swords with compatriot Jimmy Connors on the world's biggest stages.
Czech Ivan Lendl raised the bar still further, becoming almost unbeatable at the US Open, while Boris Becker and Stefan Edberg contested three consecutive Wimbledon finals.
Pete Sampras and Andre Agassi, as different as chalk and cheese on and off the court, played 34 times from 1989, culminating in Sampras's final bow when he beat his rival in the 2002 US Open final, his 14th Grand Slam title.
EIGHTH MAJOR
Although Agassi claimed his eighth major title at the Australian Open title in 2003, there is no doubt he missed having his old sparring partner in his sights.
Sampras also benefited. When Aggasi returned from his self-imposed break in the late 90s, he sent the Las Vegan a note expressing his relief that he was back.
In the biography "On being John McEnroe" the American admits the premature retirement of Borg left a vacuum that no other rival could fill, not even Connors.
His respect for the Swede led him to try, unsuccessfully, to lure him back to the circuit.
So, while 19-year-old French Open champion Nadal was tearfully collecting his trophy in Dubai at the weekend, Federer stood at courtside, already plotting revenge.
He probably would have won it last year, only to get trampled by the marauding Spaniard in an intense semi-final.
He also lost to Nadal in Miami in 2004 and his only success against him came, also in Miami, a year later when he recovered from a two-set deficit to claim the title.
The game comes so easy for Federer that he can beat top-10 Grand Slam winners like Lleyton Hewitt and Andy Roddick with cruise control switched on.
Nadal is different. So far, at least, Federer has not worked out a way to counter the fizzing topspin and sheer tenacity of the Mallorcan matador.
"It's not easy being expected to win all the time," Federer said after losing in Dubai. "But I'm happy with my game and it gives me something to look forward to when I play him again."
For his part, Nadal keeps up his mantra that Federer is untouchable as world number one, although it is unlikely that he really believes that.
The bristling, bad-tempered showdowns of the Eighties might be asking a little too much, such is the obvious rapport between the world's top two players.
However, if they end up on opposite sides of the net on a regular basis this year, and barring injuries that will surely happen, tennis fans will be in for some epic showdowns.