The first-ever national deal offered by Groupon proved a big win for both the group-buying site and its retail partner, apparel merchant The Gap.

The Aug. 20 one-day deal sparked a 37% increase in traffic to Groupon.com over the previous day, says research director Heather Dougherty of web traffic measurement firm Experian Hitwise. And 53% of the traffic that went from Groupon, where consumers could purchase a $50 Gap voucher for $25, to Gap.com were consumers who had not visited Gap.com in the previous 30 days, Dougherty says. That suggests the apparel retailer attracted new customers through the offer, which was redeemable only in Gap bricks-and-mortar stores.

Groupon says 441,000 consumers purchased the $50 Gap vouchers. It was the first national deal offer for Groupon, which typically offers discounts on products and services in several major cities. “The national offers are a good strategy for group buying websites to pursue to attract a broader audience in locations where they may not have a presence yet,” Dougherty writes in a blog post.

Groupon captured 50% of the traffic to group-buying web sites for the week ended Aug. 21, which included the period of the Gap offer, Hitwise says. During that same week, the share of all Internet traffic that went to those group-buying sites was up 416% over the same week last year, according to Hitwise.