The 29-year-old Vinci was down early in the first set, but roared back to vanquish Michaella Krajicek 6-2, 6-0, in a match which lasted just 57 minutes on the red clay at The Fairmont Acapulco Princess.
Italy's Pennetta needed slightly longer -- 66 minutes to be exact -- to send her opponent, Colombia's Mariana Duque-Marino, packing thanks to a 6-0, 6-4 triumph.
The Mexican Open stalwart 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.
Meanwhile, third-seeded Italian Sara Errani earned a semifinal meeting against Vinci with a 6-4, 6-3 spanking of Spanish lucky-loser Estrella Cabeza Candela.
Romanian four-seed Irina-Camelia Begu breezed past Slovakian Magdalena Rybarikova 6-1, 6-2 in the late match. She will face Pennetta in the semis.
This year's Acapulco champion will collect $37,000.