The Australian model and race ambassador, who gave birth to Oscar three months ago, said that she was excited to be spending the day at Melbourne Cup with her sports star husband Chris as her mother looked after their son.
Rebecca told the Herald Sun: "It will be really nice to be with Chris today. It's the biggest race of the year and it's such an electric atmosphere."
She revealed that she "got up at 6am" to get ready for the races and Oscar "woke up at 6.15am", joking: "I beat him for once."
Rebecca, wearing a royal blue headpiece designed by Richard Nylon and a yellow Sass & Bide dress, was photographed with her sister Kate Twigley and her boyfriend Matt Seal, who were both due to join the Judds in the Myer marquee later in the day.
Supermodel Jennifer Hawkins was also spotted wearing emerald green at Flemington with fiancé Jake Wall.
Dita Von Teese was spotted at a racing event earlier this week, while Sarah Jessica Parker is scheduled to attend Oaks Day on Thursday.