LONDON — Sanya Richards-Ross accelerated through the stretch to win the Olympic 400-meter race Sunday for the first US gold in track and field at the London Games.

Capping a four-year wait for a second chance with the finish she wanted, Richards-Ross won in 49.55 to edge out the defending champion, Christine Ohuruogu of Britain, who finished in 49.70.

American DeeDee Trotter finished third in 49.72.

Richards-Ross ran to the stands and hugged her husband, Jacksonville Jaguars defensive back Aaron Ross, a quite different scene from 2008 in Beijing, when she finished third and was found crying under the stands at the Bird’s Nest.