Williams, the No.3 seed and a two-time former champion at the Open, had a tough time closing out the first set - she let a 4-1 lead get to 4-all before tucking it away - but she was brilliant in the second set, 18 winners to just five errors.
"I definitely missed being on the court this summer," said Williams, who missed the summer hardcourt lead-up due to a knee injury. "I did land on my leg, but thankfully after that she did most of the running, so that helped me a lot."
Williams fired a 124mph ace on the first point of the match, not such a bad return to match play: "It was a great way to start off. I love playing the night match. It was fun - even more fun when the points were going my way."
World No.1 Serena Williams had to withdraw from this year's Open with a foot injury. Her big sister was asked about that, too: "It definitely affects the doubles draw, too. It's just not the same, but that's sport. Sometimes you have to deal with injury, but you just come back stronger. I know she will."
With her win over Vinci, Williams became the fifth player in the Open Era to record 200 Grand Slam match wins (Martina Navratilova, Chris Evert, Steffi Graf and Arantxa Sánchez-Vicario also surpassed that milestone).
The highest-ranked American not named Williams, Melanie Oudin, the darling of last year's Open, also advanced, putting on an impressive mix of aggression and counterpunching to beat Olga Savchuk in the morning, 6-3 6-0.
"It was a real honor to start the US Open off on Ashe, first match. It was cool. I didn't expect that," said Oudin, who made a Cinderella run to the quarters here last year. "I thought I had a really solid match. I was really nervous at the start but I got it out in the first set. In the second set I played really well."
Oudin lost two points in the second set and was asked about the near golden set during her post-match press: "I didn't think about it until I was up 4-0, but then I did. I shouldn't have. I think maybe I would have gotten it."
Other seeds advancing included No.10 seed Victoria Azarenka, No.12 seed Elena Dementieva, No.13 seed Marion Bartoli and No.16 seed Shahar Peer. No.24 seed Daniela Hantuchova avenged a first round loss in New Haven a week ago, beating Dinara Safina, 6-3 6-4. Another former No.1, Ana Ivanovic, made a solid start, snapping a four-match losing streak to lefties by beating Ekaterina Makarova comprehensively in straight sets, 6-3 6-2.
"It was a real honor to start the US Open off on Ashe, first match. It was cool. I didn't expect that," said Oudin, who made a Cinderella run to the quarters here last year. "I thought I had a really solid match. I was really nervous at the start but I got it out in the first set. In the second set I played really well."
Oudin lost two points in the second set and was asked about the near golden set during her post-match press: "I didn't think about it until I was up 4-0, but then I did. I shouldn't have. I think maybe I would have gotten it."
Other seeds advancing included No.10 seed Victoria Azarenka, No.12 seed Elena Dementieva, No.13 seed Marion Bartoli and No.16 seed Shahar Peer. No.24 seed Daniela Hantuchova avenged a first round loss in New Haven a week ago, beating Dinara Safina, 6-3 6-4. Another former No.1, Ana Ivanovic, made a solid start, snapping a four-match losing streak to lefties by beating Ekaterina Makarova comprehensively in straight sets, 6-3 6-2.