Sainsbury's online business took more than£10 million in sales from market leader Tesco.com last year, as the grocers jostled for position.
Sainsbury's to You also grabbed sales from Asda, Safeway and Iceland's e-tail arms, according to customer switching data from TNS.
For the 52 weeks to February 2, Sainsbury's to You won£10.4 million in sales from Tesco.com.
A Sainsbury's spokeswoman said: 'We are pleased that consumers are recognising what we think is a superior online shopping service.'
She added that in the past 12 months Sainsbury's had increased the number of stores from which orders are fulfilled by 20 stores to 71. The grocer now reaches 75 per cent of the population, while Tesco.com has 95 per cent coverage.
Tesco.com chief executive John Browett was not concerned by the data. He said: 'Sainsbury's rolled out last year, so that's where the growth came from, but we are still the clear market leader.'
Ocado was the only e-grocer to take sales from Sainsbury's, to the tune of£2 million. Joint managing director Nigel Robertson said that Ocado is delivering 1,000 orders a day to a catchment of 2 million households in the Southeast.
Tesco.com generates sales in excess of£350 million a year, and Sainsbury's to You announced annual sales of£110 million last year.