Fourth seed Dokic, who lost her first match of the year in the Pan Pacific Open to Anne Kremer of Luxembourg, needed just 42 minutes to dispose of her Spanish opponent, who is ranked 30th in the world.
“She’s in the top 30 so to beat her that comfortably has given me confidence,” Dokic said.
The 18-year-old Yugoslav, who has said she needed to build up her strength to compete with the big hitters at the top of the game, turned up the power as the match progressed, hitting the ball with mounting aggression.
She broke her opponent outright in the second set and kept the pressure on to move 5-1 ahead before wrapping up the match with a superb volley into the corner.
In the first set, the players held serve until Dokic broke to lead 5-3 and she sealed the set with a clinical drop-shot.
Dokic said she had been working hard on her serve and was encouraged by her performance.
Dokic missed last month’s Australian Open, citing concerns that her controversial father Damir might be unwelcome in Melbourne after he fell out with tournament organisers last year.
Dokic left her adopted homeland Australia as a result of the fallout to play under the flag of her native Yugoslavia.
She will meet eighth seed Elena Dementieva of Russia in the quarterfinals.
Jelena Dokic (Yugoslavia) bt Cristina Torrens Valero (Spain) 6-3 6-2; 8-Elena Dementieva (Russia) bt Greta Arn (Germany) 7-6 6-4; Francesca Schiavone (Italy) bt Daniela Hantuchova (Slovakia) 6-2 7-5.—Reuters