Supervalu has maintained the biggest share of the country's grocery spend, according to Kantar Worldpanel, but the market as a whole saw limited growth as supermarkets continued to cut prices.
In the 12 weeks to the 23rd April Supervalu had 22.8% of the total grocery market, down slightly on the same period of 2016.
Dunnes had a 22.1% share during the same period - up 0.6 percentage points year-on-year - with Tesco's share falling to 21.6% - a decline of 0.6 percentage points.
Meanwhile discounters Lidl and Aldi held steady in the year, taking 11.3% and 11% of the market respectively.
However average sales value was only 2.3% higher than last year, with price deflation of 0.3% keeping a lid on supermarket revenues.
Dunnes enjoyed the biggest rise in sales values, up 5.1% in the year, while Aldi's rose by 3%.
Lidl's sales were up 2.4% while Supervalu saw gains of 1.8% compared to a year ago.
Tesco was the only major retailer to see a decline in sales value, according to the survey, down 0.6% in the survey.
Kantar Worldpanel said the decline in prices was reflective of a trend away from promotional discounts and towards longer-term price cuts.
It said that just a quarter of all goods are now bought on promotion - compared to a third in 2014.