A battling Aryna Sabalenka credited new a “mental toughness” on Sunday for helping her survive an Australian Open first-set wobble that a few years ago might have cost her the match.

The two-time defending champion beat Sloane Stephens 6-3, 6-2 in the first round to begin her bid for a historic hat-trick at Melbourne Park. But the Belarusian did not have it all her own way against the 2017 US Open champion on Rod Laver Arena.