Schiavone defeated Venus 7-5, 7-3, then countered a strong comeback from Serena to defeat the younger sibling 7-3, 8-10, 8-6.
Flavia Pennetta also beat Venus, whose strap broke on her dress before a sellout crowd of 11,000. Venus dashed off the court and returned in her third outfit of the event. She also brought popcorn to share with Pennetta, who won 7-6, 7-2.
Serena defeated Pennetta 6-8, 7-3, 7-3 before the Williams sisters won the doubles 3-7, 8-6, 8-6.
The Italian pair delighted the crowd in the warmup by dancing to Michael Jackson's "Thriller."
Venus has played just once since pulling out of the U.S. Open three months ago because of an immune system disease. Venus defeated Serena in an exhibition match in Colombia last week.