Those wondering just why Serena Williams has been more successful than her older and more athletic sister Venus throughout their respective glittering tennis careers received their answer at Melbourne Park on Wednesday.
As the pair has wracked up countless major singles titles between them and doubles' titles together during their ten years of dominance of women's tennis, the question of just when their dominance will finally come to an end has also been constantly asked.
Well on quarter-final day of the 2010 Australian Open it almost happened but the fact that it didn't also answers the question as to why Serena will be remembered as the greater player of the pair.
With Venus set to turn 30 this year and Serena, 29 it is only natural the pair will find it harder to maintain their Grand Slam dominance which began when Serena won the US Open just a few weeks short of her 18th birthday in 1999.
But these days the pair has to work far harder for victories at the business ends of major tournaments.
However while Serena still appears to have the fight within her to keep the challengers at bay, Venus doesn't and is playing like a player whose heart is no longer in the game.
Both faced surprisingly strong challengers from unfancied opponents in the quarter-finals on a day when most tennis fans expected both to cruise into a head-to-head semi-final clash.
However while Serena faced the tougher challenge - against No.7 seed Victoria Azarenka - while Venus was up against Chinese No.16 seed Li Na, it was Venus that faltered.
But it was the manner of their respective performances that said most about where the pair's heads are at in regards to the twilight years of their careers.
Venus was cruising against the much smaller Li after winning the first set in just 30 minutes while she served for the match in the tenth game of the second set.
Yet in a match featuring an astonishing 17 service breaks in just 33 games, it was Venus that faltered as Li ensured China would have two representatives in the semi-finals of a Grand Slam singles tournament for the first time, following Zheng Jie's win over Maria Kirilenko on Tuesday.
Serena in contrast was up against a player who could at least match her for power.
And when she trailed 4-0 in the second set after having lost the first set, it appeared that rarest of events was going to happen - both Williams' sisters being beaten in a Grand Slam event on the same day.
But Serena is made of far sterner stuff than her sister and despite having achieved everything there is to achieve in the game, simply refuses to ever concede defeat easily.
And while Venus collapsed from a seemingly unbeatable position, Serena rallied from a seemingly hopeless one to claim seven of the next nine games to win the second set in a tiebreaker before crushing Azarenka in the deciding set.
In the process she showed just why she has won every Grand Slam title - four Australian Opens, three Wimbledons, three US Opens and one French - for a total of 11 and has generally been regarded as the world's best player for most of the last decade.
Venus too showed why she has only won Grand Slam tournaments on her preferred faster surfaces - five Wimbledons and