LONDON (Reuters) - The United States' Sarah Hammer grabbed the psychological advantage over Britain's Laura Trott thanks to a scorching pursuit victory that gave her a one-point lead in the women's Olympic track cycling omnium on Tuesday.

Hammer, the world record holder and four-times world champion in the individual pursuit, lived up to her top billing to beat Trott into second place by almost a second.

Trott, who is bidding for her second gold of the Games after winning the team pursuit, has two races remaining in the six-discipline omnium to turn the tables.

Canada's Tara Whitten is in the bronze medal position, seven points adrift of Trott, with the 10kilometre scratch race and 500 meter time trial to come later on Tuesday.

(Reporting by Toby Davis; editing by Mark Meadows)