Dunnes, which has made much of its Irishness in recent months, increased its stake from 23.7% to 24.1%.
Tesco, which is spending €5m on its high-profile price-cutting campaign, has just extended its Irish border store price cuts to 11 outlets in the Dublin area. But according to Irish sources Tesco has been hit by the controversy over its decision to import some lines directly from the UK, while squeezing shelf space devoted to Irish suppliers.
Tesco admitted that since launching the new strategy, it had removed 350 Irish lines on the grounds of poor sales, but that a fifth had been restored in response to consumer demand.
Almost half the Republic's shoppers believe Dunnes stocks most Irish goods compared with one in 20 for Tesco, a survey by Empathy Research found.
"There is some negative sentiment about Tesco," says David Fitzsimons, chief executive of Retail Excellence Ireland. "One reason Dunnes has been doing well is the tagline it has been using - 'the difference is we're Irish'."
Musgrave's SuperValu has also joined the 'patriot game' with price cuts carrying the message it is "continuing to support Irish brands and Irish jobs".