The American, who is 13th seed, went through after a 6-1 6-2 victory against an opponent who simply didn’t have the firepower to compete.
Keys, whose only worry will be the match points she gave up at 5-2 in the second set, will now face either Czech 26th seed Barbora Strycova or unseeded Kazakh Yulia Putintseva in the last eight.
Keys admitted in the build-up that she had never watched Buzarnescu in action, but quickly got to grips with the unheralded 30-year-old who was playing in the fourth round of a Grand Slam for the first time.
Striking the ball cleanly and powerfully in perfect conditions on Court Philippe Chatrier, the big-serving Keys bagged the opener in the blink of an eye against an overpowered opponent offering little resistance.
It was pretty much the same story in the second set before Buzarnescu's late resurgence which caused some anxiety in the Keys camp. The Romanian clawed back from 1-5 to 4-5 but Keys shut down the mini revival to serve for victory.
The 23-year-old Keys will now be eyeing a semi-final spot, with Czech 26th seed Strycova or Putintseva waiting in the quarter-finals.