Barty eased past Marketa Vondrousova 6-3, 6-3 in a repeat of their final at Roland Garros last year; it was just as ruthless.
The World No.1 lost her first round match at the Brisbane International; but has dispelled those doubts heading into the Australian Open as she goes into it as one of the leading favourites.
Collins on the other hand stunned Belinda Bencic, the World No.7 6-3, 6-1; after previously defeating Sofia Kenin in the second round by the same scoreline.
They will now face off in the semi-finals and despite Barty likely being the favourite from here to claim the title, the American cannot be written off as she has produced some stunning displays in the past week.