Britain sent a mixture of youth and experience to the first instalment of the Track World Cup series since the Olympics, at the Alcides Nieto Patino velodrome, the venue which will host the 2014 World Championships.
Varnish was given the opportunity to atone for her Olympic nightmare, when she and the since retired Victoria Pendleton were disqualified.
And with new team-mate James she did not disappoint, coming home in a time of 33.734 seconds, over a second and a half clear of Japan’s Kayono Maeda and Hiroko Ishii.
Colombian pair Martha Bayona and Juliana Gavira took bronze.
It was a good evening for the hosts as their men won the team pursuit in a time of 4:05.456, nearly 2.5s clear of Russia.
The Swiss took bronze, with world record holders and Olympic champions Britain not entering a team.
Another Colombian, Fabian Puerta, won the men’s 1km time trial in a time of 1:00.982, over two seconds short of Arnaud Tournant’s world record.
There was good news for British youngster Emadi though, the Staffordshire-based 20-year-old getting silver on his World Cup debut.
Emadi, the son of academics, only started racing competitively as a teenager. France's Quentin Lefargue was third.
There was a second silver for a British team, as a Wales select of Elinor Barker, Clara Horne and Amy Roberts were beaten to team pursuit gold by the Italian team. Colombia were third. That was effectively a B-team for Britain, with none of the Olympic champions and world record holders present.
There were no Britons in the field as Australia’s Isabella King won the women’s scratch race. Jarmila Machacova of the Czech Republic was second with Elena Cecchini of Italy third.