Sainsbury's has received a boost ahead of Christmas as new figures reinforced its position as the star performer among the "big four" players.
The group hiked its share of the market once more, from 16.7% to 16.9% in the 12 weeks to November 25 after notching up the highest sales growth of the UK's four biggest chains, according to Kantar Worldpanel.
Sainsbury's rang up sales growth of 4.7% year-on-year. but the chain's performance came at the expense of its three main rivals, which saw their shares slip back on a year ago.
Asda's market share edged down from 17.5% a year earlier to 17.3%, while Tesco saw its market share slip from 31% to 30.7%. And experts predict more bad news on Wednesday, when Tesco's third-quarter trading update is expected to reveal sales falling back into the red.
Smaller rival Morrisons also endured another difficult quarter as sales fell 1.1%, which left its market share trailing at 11.7%, down from 12.3% a year earlier.
Kantar director Edward Garner said Morrisons was being held back by its absence from online grocery retailing.
"However, it is expected that online wine sales via Morrisons cellar will make a start on addressing this," he said.
Sainsbury's has enjoyed a continued sales boost in recent months, helped by its Paralympics sponsorship and investment in cheaper own brands.
While Tesco recently reported its first fall in profits for two decades, Sainsbury's last month posted a 5% rise in half-year profits to £373 million. It is waging war with money-off coupons, printing nearly 250 million Brand Match vouchers since the scheme's launch a year ago.
But Tesco has failed to keep pace and analysts expect the chain to report sales falling back into negative territory in its third quarter, with experts at Nomura pencilling in a drop of 0.9%.