Her coach admits to "coaching" during the match.
Williams has made headlines for coming to blows with umpire Carlos Ramos after he gave her a coaching violation in the second set.
The tennis legend, who was then docked a point after she smashed her racket, told Ramos she would rather lose than cheat.
'I'm honest, I was coaching,' Mouratoglou said after the game. 'I don't think she looked at me, so that's why she didn't even think I was.'