The world No. 9 beat Carla Suarez Navarro 6-3, 3-6, 6-1 to book her place in the quarter-finals at the 2017 US Open.
Williams, 37, has now taken her record in majors to 19-3 this year with her win over the Spaniard.
And when asked about her longevity and what motivates her to succeed, she put it down to her sister Serena and the rest of her family.
Serena said: “I don’t know. If I did I would put it in a box and sell it.
“I love the game and you’ve got to have health, fitness, skill, desire and the love.
“My sister motivates me a lot and my family too.
She also gave some fighting talk after reaching her 39th career quarter-final by insisting she he is here to take the US Open title.
“For me I’m focused on myself and try to be aggressive as possible,” Williams added.
“Nobody ever gives you a Slam, you’ve got to take it – so I’m going to try and take it.
Up next for the American at Flushing Meadows is a clash with either Garbine Muguruza or Petra Kvitova.