The world No.8 won in straight sets against last year's quarter-finals 6-3 7-5 on Thursday afternoon. 

The opening set went serve for serve in the first seven games with neither player facing breakpoint or deuce until Barty earned the break in the eighth game. 

Barty never held match point in the second set with Keys fighting to stay alive at 5-4 but at 6-5 the Australian cruised through the game to seal her spot in the Semi-final.

The American racked up 26 unforced errors in a match which last just over an hour. 

Barty is the first Australian to reach the semifinals at Roland Garros in three years, Sam Stosur being the last, and current WTA live rankings put the 23-year-old on course to reach No.4 in the world.

She will face another American in teenage sensation Amanda Anisimova, who beat reigning champion Simona Halep.

"Anisimova has been playing some great tennis, to reach a semi-final you must be doing the right things," Barty said on court.

"It's an exciting opportunity for both us and we will both enjoy it tomorrow."

The game is set to be played first up on Friday morning (11am CEST).