In a quarter-final clash postponed on Wednesday because of heavy rain, Barty produced an intelligent display full of guile in the Court Suzanne Lenglen sunshine.
Barty's greater variety proved too much for 2018 semi-finalist Keys whose power game broke down at the vital moments.
The only blemish came when she failed to serve out the match in the second set but she recovered her poise to complete victory and set up a semi-final against American teenager Amanda Anisimova, who beat reigning champion Simona Halep.
"It was a really clean match," Barty, who returned to the sport three years ago after stopping to play cricket, told reporters. "I felt I was in control.
"I got the balls I wanted, and I was able to put the balls in difficult positions for Maddie. Really, really happy with how we went about it."
While 14th seed Keys, bidding to reach her fifth Grand Slam semi-final, usually overpowers opponents with her potent serve and flat groundstrokes, Barty prefers to use her range of slice, topspin and clever placement to outfox her rivals.
She seized control of the match in the seventh game when Keys struck a backhand wide at 30-30, then the American failed to punish a short ball and Barty, who had stood her ground in the left corner, smashed a stunning backhand winner to break.
Keys was looking flustered and short of ideas but she produced a venomous forehand winner to hold for 2-2 in the second set after Barty had earned a break point with a loopy, angled forehand that dragged Keys way out of court.
Barty's sliced backhand is one of the best on the women's tour and she used it to cutting effect to drag Keys into areas of the court she did not want to be.
Keys lost patience at 3-3 and blazed a forehand long, then a backhand to offer up the break of serve.
Barty had not even faced a break point on her own serve but with victory in sight at 5-4, she finally let the nerves show with a double-fault and then a forehand error to gift Keys a lifeline that had looked unlikely.
Keys could hardly believe that she had been handed a lifeline but she failed to grab it dropped serve immediately with a double fault to allow Barty to serve for the match again.
This time she reeled off four straight points to reach the semi-finals.
She is the highest-ranked player left but Barty knows there is still a long way to go before Saturday's final and first she must do her homework for a semi-final against Anisimova, whom she has seen in action for all of 20 minutes.
"I'll sit down with my coach tonight and try and work out a game plan, try and work out ways that I can be effective against her," the 23-year-old Queenslander said.
"It's a new situation for me. It's a little bit of a new
territory. But I will prepare and do the best that I can to keep it normal."
(Reporting by Martyn Herman, editing by Pritha Sarkar)
