They are by no means the first pair of 30-somethings to be ranked No. 1 and No. 2. Still, their late-career reign over women's tennis is impressive.
Even with a slew of next-big-thing players like Eugenie Bouchard, Simona Halep and Sloane Stephens trying to knock them off, Williams and Li have played more consistently solid tennis than the rest of the field.
How are they doing this? All good things must come to an end, right?
Eventually, Father Time will impede their progress and the other players will catch up. Until then, the younger up-and-comers, the withering challengers and barely hangers on need to take note. Right now, Williams and Li, a couple of 30-something women, are simply better than the rest.