Barker, riding for Welsh Cycling's trade squad Team USN, began the third and final World Cup of the season by claiming team pursuit bronze with Amy Roberts and Ciara Horne.
And the 18-year-old, who claimed the world junior time trial title in Limburg back in September, returned to the boards on day two of three in Aguascalientes for the women's omnium.
She started off in fine form, setting a personal best of 14.560seconds in the flying lap to place 12th before finishing 15th in the points race where she collected three sprint points.
Barker was then the fifth rider to go in the elimination race to place 17th with three events remaining on Sunday and Sarah Hammer, who won Olympic omnium silver behind Britain's Laura Trott at London 2012, leading.
Meanwhile Mould, who was 15th in the flying lap, sixth in the points race and eighth in the elimination race as the men's omnium began on day one, started day two with the individual pursuit.
The Welsh cyclist placed 20th in the individual pursuit before illness prevented him from completing the scratch race and time trial as Russia's Artur Ershov cruised to gold.
Horne was also in action on day two in Aguascalientes however she failed to qualify for a medal ride off in the individual pursuit, placing 11th overall.