The second seeded American, who appears to have found her form again after struggling in the early stages of her comeback from a six-month injury break, made a hesitant start before dominating her frustrated opponent from Colombia.

Often unable to put her first serve into play, Williams was tested by an opponent who thrives on clay. Despite breaking to love to lead 2-0 with three returns and a crosscourt forehand winner, Williams double-faulted to allow Zuluaga to recover the break in the next game.

Battling to stay in contention against Zuluaga's strong forehand and greater consistency, Williams saved three break points at 2-2, but then lost her serve to love at 4-4 and failed to convert a break point as Zuluaga served out for the set.

But Williams swiftly turned the match around in the second set. Finding greater accuracy with her serve and rallying more aggressively, she dropped just one point in her first three service games and swiftly built a 5-1 lead.

Although she then lost her serve and had to break again to level the match, and then had to survive two break points as the deciding set got underway, Williams didn't look back after taking a 2-0 lead on her fourth break point.

Top seed and defending champion Amelie Mauresmo will face Eleni Daniilidou of Greece in the second round on Thursday, after Daniilidou dismissed Argentine Gisela Dulko 6-2, 6-2 by winning the last four games of each set.

Italian sixth seed Silvia Farina-Elia beat Denisa Chladkova of the Czech Republic 6-4, 6-1, winning four straight games in the first set and conceding just four points in four games at one stage of the second.

There were also first round wins for seventh seed Patty Schnyder, who beat Elena Tatarkova 6-3, 6-4, and Magdalena Maleeva, who beat Elena Likhovtseva 6-3, 6-1.

Francesca Schiavone, who was given the number nine seed when fifth seed Paola Suarez withdrew, overwhelmed Tina Pisnik 6-3, 6-0, and Lenka Nemeckova won 6-3, 6-2 against Henrieta Nagyova.

In a second round match, eighth seed Anna Smashnova-Pistolesi beat Daniela Hantuchova 6-4, 7-5.