Aldi, Lidl, Iceland and Farmfoods have all stolen customer spend from the rest of the grocery market in the 12 weeks to 22 March compared with the same period the previous year.
But Netto's sales were hit, having lost more than £3m in that period to other retailers.
The big four took most of the sales lost by Netto, although it also lost to the other discounters and Marks & Spencer.
Netto was losing out for a number of reasons, including the quality of its offer and the location of its stores, analysts said.
"Netto has been the poor cousin of the discounters," said Shore Capital head of research Clive Black. "Aldi is setting the pace - it opens a lot of stores in middle class areas, which are not traditionally the territory of the discounters. Netto's stores are located in much lower demographic areas, and this is a white collar recession. It is having a bigger impact on the middle classes, who are being won over by the likes of Aldi and Asda."
Netto didn't have the buying power of the other discounters, he added, and had suffered from a lack of continuity of management following the departure of its MD Richard Lancaster last year, who was replaced by Charles Kay.
Netto was not famous for quality, whereas Aldi was building a reputation for its own label, said Verdict analyst Malcolm Pinkerton. "Netto is perceived as a hard discounter, but people don't want to sacrifice too much quality. Aldi and Lidl have a better reputation for quality."
While Asda was the biggest winner value-wise, swiping £115m of spend from its rivals, Aldi was the only retailer to have gained at the expense of every retailer. Aldi grabbed £31m of sales, while Lidl won £13m, and Iceland and Farmfoods each won £5m of sales.
Netto declined to comment on the figures, but has previously disputed TNS data.