Kevin Barnes, marketing manager for online underwear retailer UnderU.com, said that week-on-week sales for Emporio Armani products were up 20%.
"It's definitely down to the attention given to the brand as a result of pictures of the ad [in newspapers]," he said.
"When the product actually comes in for next season, sales are likely to be even better. It's been great for awareness of the brand."
Department store group Selfridges, which also stocks the range, said it had seen an even more pronounced 30% rise in sales of Emporio Armani underwear, with white briefs in general up 50%, outselling boxer shorts by two to one.
The advertising campaign featuring the footballer is set to break in February. It is part of a three-year deal for which 32-year-old Beckham is reportedly being paid £20 million.
The campaign was shot by photographers Mert Alas and Marcus Piggott, who have worked for other luxury fashion brands including Louis Vuitton, Missoni, Roberto Cavalli, Fendi and Miu Miu. The ad will break in the February edition of US Vanity Fair before being rolled out globally in magazines and on billboards, including in the UK.
Beckham’s wife Victoria has recently linked up with US lingerie chain Victoria’s Secret as part of the Spice Girls’ comeback tour.