Tesco and Aldi were the fastest-growing grocery retailers in the Irish market in the 12 weeks to 13 August, according to new figures from Kantar Worldpanel.
Both retailers had growth of 3.4% for the period.
Despite the strong growth, Tesco remains the country’s second-largest grocery retailer, with a market share of 22.0%.
SuperValu, at 22.5%, has the largest share of shoppers and had growth of 0.4% during the period.
Dunnes Stores is third with a 21.1% market share, after growth of 2% in the most recent 12-week period.
Despite its recent strong growth, Aldi is still behind its German low-cost competitor Lidl.
Lidl - with growth of 2.7% - has a market share of 12%, compared with Aldi’s 11.5%.
Overall in the 12 weeks to 13 August, the Irish grocery market saw deflation of 0.5%.
Commenting on the latest figures, Director at Kantar Worldpanel David Berry said: "A year-on-year sales growth of 0.4% was enough for SuperValu to hold onto the top spot in the face of a strong challenge from Tesco.
"SuperValu has improved the number of items sold per trip but has done so at a lower price point and now holds a 22.2% share of the grocery market, down 0.3 percentage points on last year.
"This is the fourth consecutive period of growth for Tesco, which is a clear indication that it's achieved a turnaround in performance. This is also only the second time since July 2014 that Tesco has posted a year-on-year increase in market share."
Separately, Aldi announced today it has increased its support for small suppliers by reducing its payment terms to 14 days.
The new terms apply to all suppliers that transact up to €300,000 worth of business annually with the low-cost retailer and are effective from 11 September.
Aldi said more than 100 businesses will immediately benefit from the change.