Sainsbury's has reported a 0.4% fall in its like-for-like sales over the Christmas period.
Despite the slump. the supermarket's chief executive Mike Coupe said its performance over the three months to 9 January was an improvement on the past two quarters.
He added that in the seven days prior to Christmas, transactions were up 2.6% to 30 million.
Mr Coupe said the second half of Sainsbury's financial year is likely to be stronger than the first, but warned that "food deflation and pressures on pricing will ensure that the market remains challenging for the foreseeable future"
Yesterday (Tuesday), Morrisons was the first of the 'big four' supermarkets to publish its Christmas results - surprising analysts with a 0.2% rise.
Retail analysts Kantar Worldpanel said: "Sainsbury's is making the right moves in simplifying its pricing and strategy and reducing multi-buy offers."
According to Kantar's figures, Sainsbury's was the only one of the big four supermarkets to increase its market share during the Christmas period. Its share rose 1 percentage point to 17%.