By Sarah Nassauer, Market Watch–

Americans jumped on holiday deals over the weekend but a larger slice of their spending migrated online, often through mobile devices, highlighting the high-wire act that faces retailers tethered to stores.

A National Retail Federation survey released Sunday showed that online spending during Thanksgiving weekend grew at the expense of store spending for a straight second year. The NRF survey estimates that about 109 million people shopped online, compared with 99 million in stores.

Foot traffic at malls and shopping centers was thinner than the frenzied crowds of years past after retailers offered discounts earlier in November and many of the promotions also were available online.

Online spending on Thanksgiving and the following day, known as Black Friday, increased nearly 18% to $5.27 billion compared with last year, said Adobe Systems Inc. ADBE, -0.32%  , which analyzed data from 22.6 billion visits to retail websites. More Americans think it is “easier to shop from one’s couch than to fight one’s way through the mall,” Ray Harjen, a spokesman for RetailNext, an in-store analytics firm, which reported that the number of store visitors fell nearly 11% on Black Friday from a year ago and sales dropped more than 10%.