Serena Williams could be set for her stiffest challenge so far at this year's US Open when she faces fellow American and 2017 champion Sloane Stephens for a place in the last 16.
The pair have played each other six times, with 38-year-old Williams coming out on top on five occasions, including at the 2013 US Open, which she won.
However, this is their first meeting since the 2015 French Open.
"She's a great competitor," said the 23-time Grand Slam singles winner.
"You can't win a Slam and not be really, really, really, really good.