Trott, 24, went into the final points race boasting a 26-point lead after winning the flying lap to go with the elimination race and individual pursuit, having come second in the scratch race and the time trial too.
The most decorated woman in British Olympic history, who also won the team pursuit earlier in the Games, was never really troubled as she warded off any danger and picked up plenty of points in sprints.
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“I can’t believe it. I don’t want to cry on television,” said Trott to the BBC, before breaking down in tears.
“I did not expect that at all, I’m just so happy that it all came together.
“I honestly can’t thank people at home enough. To be able to repeat my success in London… I can’t explain it.”
Parnter Jason Kenny is in the final of the Keirin and if he wins, he will draw level with Sir Chris Hoy on six golds and one bronze to become the joint most decorated British Olympian.

Afternoon session:

Trott set the second fastest time in 500m time trial to lead on 156 points, ahead of Jolien D'Hoore (144) and Sarah Hammer (140).
Australia's Annette Edmondson set the fastest time in the time trial, and sits in fourth on 130 points.
Just two events stand between Trott and a fourth gold, with the flying lap and points race taking place at the velodrome tonight.
On Monday Trott, 24, finished second in the scratch race before winning the individual pursuit and elimination events.
The track programme concludes at the Rio velodrome on Tuesday when, as well as the omnium, the women's sprint and men's keirin will also be decided.
Britain have won four of the seven titles so far and could be set for more with Rebecca James and Katy Marchant both into the semi-finals of the sprint.
James is up against Elis Ligtlee of the Netherlands, who beat her to gold in the kierin, while Marchant faces twice world champion Kristina Voegel of Germany. Voegel, at 25, is the oldest of the four qualifiers, who have an average age of 23.
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