Former world number one Serena Williams looked well short of her best as she struggled to a 7-5, 6-3 victory over Spain's Maria Sanchez-Lorenzo in the Rome Masters second round on Tuesday.

The American top seed, who is working her way back to fitness after an eight-month injury layoff, made an error-strewn start to gift the Spaniard an early break of serve.

Williams faced two more break points in the third game and then found her range, dragging Sanchez-Lorenzo round the court with hard, flat groundstrokes to race into a 5-2 lead.

Sanchez-Lorenzo pulled a break back but aggressive returning by Williams in the 12th game earned a chance to seize the set, which she did with a powerful drive-volley.

Having exchanged early breaks in the second set, Williams gained the decisive break in the sixth game, when a backhand pass and forehand crosscourt winner gave her a 4-2 lead, and she held serve to close out the match,

"It was a struggle today. I hit a lot of fly-balls, but so long as I won that's OK," Williams told reporters.

Asked whether her inconsistent performance was due to injury or her lack of competitive play, Williams replied: "I haven't played in a little while. Physically I'm OK, I just need match practice."