Williams, the top seed and Madrid champion in 2012 and 2013, needed just 55 minutes in a 6-0, 6-1 pounding of fellow American Madison Brengle, while the third-seeded Sharapova also had an easy opener with a 6-2, 6-3 triumph over Switzerland's Timea Bacsinszky.
Williams won the first set in 21 minutes, then grudgingly ceded a game to Brengle before quickly regaining focus. Brengle saved five break points in the first game of the second set.
"I was able to win good today, but she's been playing really well," Williams said. "I've been following her results. She got to the semifinals of her last clay-court event and she's been having some good wins."
Next up for Williams will be another fellow American in Sloane Stephens, who won her first-round match on Saturday in three sets against countrymate Bethanie Mattek-Sands.
Venus Williams was not as fortunate as her sister. She had a tough first-round match with Victoria Azarenka and the former world No. 1 from Belarus notched a 6-3, 7-5 victory. Azarenka could face Serena Williams in the third round.
Other seeded winners Sunday included 2011 champion Petra Kvitova and Caroline Wozniacki. The fourth-seeded Kvitova had to rally for a 3-6, 6-1, 6-4 win over qualifier Olga Govortsova of Belarus, while the fifth-seed Wozniacki made short work of Australia's Jarmila Gajdosova, 6-3, 6-0.
Canada's Genie Bouchard and Germany's Angelique Kerber were also upset victims on Day 2 at the Magic Box. Barbora Strycova of the Czech Republic rebounded from an awful first set to claim a 0-6, 6-3, 6-3 win over the sixth-seeded Bouchard, while former U.S. Open champ Samantha Stosur of Australia took out the 12th-seeded Kerber, 4-6, 6-3, 6-3.
The 10th-seeded Suarez Navarro topped Zarina Diyas, 6-4, 6-4, the 11th-seeded Petkovic edged Italy's Flavia Pennetta, 6-3, 7-5 and the 14th-seeded Pliskova, coming off a title Saturday in Prague, blasted Spain's Silvia Soler Espinoza, 6-1, 6-2. Errani, the 15th seed, had won the first three games of her match against Paula Badosa Gibert when the Spanish qualifier retired.
Elina Svitolina of the Ukraine followed up her Marrakech title from Saturday with a 6-0, 6-3 rout of Slovak veteran Daniela Hantuchova to earn a second- round matchup with Ana Ivanovic, a Saturday first-round winner.
Second-round play begins Monday with Serena Williams and Stephens set to open the night session. Daytime matches feature Wozniacki against American qualifier Christine McHale, a 6-3, 6-2 winner Sunday against Germany's Mona Barthel, and ninth-seeded Agnieszka Radwanska of Poland against Australia's Casey Dellacqua -- both of whom won Saturday.