The 18-year-old, the youngest player in 15 years to win a Masters event last week in Monte Carlo, faces Argentine Agustin Calleri, who edged to an absorbing 6-4, 6-7, 7-6 victory over his fellow countryman and fourth seed Guillermo Coria.
Nadal turned in another irresistible display to record his first victory in four attempts against Hrbaty.
Aggressively competing for every point, the Spaniard gave his opponent little chance as he reeled off a string of precise two-handed backhands and spectacular running passes on his way to an emphatic victory.
Former world number one Juan Carlos Ferrero continued his revival with a comfortable 6-1, 6-2 win over fellow Spaniard Alberto Martin, who had knocked out defending champion Tommy Robredo on Wednesday.
Ferrero, a semi-finalist in last week's Monte Carlo Masters, gave no quarter as he ripped through the first set in under half an hour.
Although he wobbled a little on his own serve in the second set, his combination of precision ground strokes and delicate drop shots earned him three breaks as he ran out an easy winner over his Barcelona-born opponent.
The 25-year-old faces an intriguing quarter-final against number two seed Gaston Gaudio or in-form Spaniard David Ferrer.
FIERCE CONTEST
Radek Stepanek of the Czech Republic sneaked a 6-7, 7-6, 7-6 win over fifth-seeded Argentine Guillermo Canas in a fiercely contested encounter on court one.
Calleri, who earned tough victories over French teenager Gael Monfils and fellow countryman Juan Ignacio Chela in previous rounds, had to fight hard against Coria to book his quarter-final place in a match lasting two hours 45 minutes.
The 28-year-old took the first set thanks to a second break in the seventh game and played compact tennis to keep the pressure on his younger opponent.
The two claycourt specialists struggled on their own serve in the second set, exchanging eight breaks in the first nine games on the way to the tiebreak, which Coria won after Calleri missed his chance with a volley error at the net.
Coria, who lost to Nadal in the Monte Carlo final, gained the upper hand in the third set as he worked Calleri around the court and broke him for a 4-2 lead.
The hard-hitting Calleri refused to fold, however, breaking back when Coria was serving for the match in the 10th game before forcing a final tiebreak which he won when returns of serve forced Coria into two backhand errors.
"I knew this one would be tough," Coria said. "It could have gone either way, but he made the most of his chances and played very well in the final tiebreak."
