The United States' Sarah Hammer edged closer to an Olympic gold medal in the women's track cycling omnium with second place in the scratch race on Tuesday.

Hammer finished second in the 10 kilometre ride, a place ahead of rival Laura Trott, to increase her overall lead on the Briton by two points with only the 500m time trial to come.

Earlier in the day the American had grabbed the psychological advantage over Trott thanks to a scorching pursuit victory.

Hammer, the world record holder and four-time 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, must now finish at least three places better than Hammer in the time trial to guarantee the title.

Australia's Annette Edmondson won the scratch race and is in the bronze medal position, five points adrift of Trott.