Top seeds Roberta Vinci and Flavia round wins Tuesday at the $220,000 Mexican Open.
Vinci, the No. 1 seed, got past Spaniard Silvia Soler-Espinosa 6-2, 7-6 (7-5) on the red clay at The Fairmont Acapulco Princess.
Later, the second-seeded Pennetta cruised to a 6-4, 6-2 victory over Arantxa Parra Santonja of Spain.
Pennetta won this event in 2005 and 2008 and was runner-up in 2004, 2006, 2007 and 2009. She's appeared in six of the last eight finals at the tournament.
Third-seeded Italian Sara Errani also eased into the second round by pasting American Irina Falconi 6-1, 6-1 in just 67 minutes; but No. 5 seed Alexandra Dulgheru of Romania was upset in three sets by Slovakian Magdalena Rybarikova, who earned a 2-6, 7-5, 7-6 (7-3) win.
Meanwhile, No. 6 Johanna Larsson of Sweden overcame Bulgarian qualifier Sesil Karatantcheva 1-6, 6-4, 6-3.
Defending Acapulco champion Gisela Dulko, seeded seventh, pulled out of the draw Tuesday due to an illness. Dulko topped Spaniard Parra Santonja in last year's Acapulco finale.
Dulko's replacement, Spanish lucky-loser Estrella Cabeza Candela, advanced by handling compatriot Lourdes Dominguez Lino, 6-4, 6-4.