The two grocers slipped on a day when the wider FTSE 100 Index edged only narrowly ahead by 7.9 points to 6830.7 as a rally during the previous session, inspired by US consumer confidence data showing a seven-year high, came to an end.
Markets elsewhere were also little changed, with France's Cac 40 flat, Germany's Dax down slightly, and New York's Dow Jones Industrial Average marginally ahead at the time of the close in London.
On currency markets, sterling was a little firmer against the greenback to just below $1.66 as it eased lower ahead of American GDP data tomorrow. The pound was flat against the single currency at just under 1.26 euros.
In London, the major listed grocers were in focus after latest till roll figures from Kantar Worldpanel revealed supermarket price inflation fell for the 11th quarter in a row to stand at 0.2 per cent in the 12 weeks to August 17.
Sainsbury's, which saw its market share drop to 16.4 per cent as its sales growth lagged behind the market, was the biggest faller in the FTSE 100 as its shares dipped nearly three per cent or 8.1p to 304.2p.
Tesco was under pressure after Kantar said the market leader's sales fell four per cent, the biggest decline among the big four chains, in a period when 53 per cent of UK households visited Aldi or Lidl at least once.
Shares dropped 2.8p to 249.3p as Kantar said Tesco's market share fell to 28.8 per cent from 30.2 per cent over the 12 months.
Morrisons, which in March promised to spend £1 billion cutting prices over three years, saw its sales fall 1.9 per cent and its market share slip to 11 per cent from 11.3 per cent. However, shares were 2.6p higher at 184.4p, having fallen 29 per cent so far this year.
In corporate news, shares in estate agency chain Foxtons fell sharply after it warned regulation will cool the housing market in the second half of this year. Profits lifted 57.1 per cent to £23.1 million in the half year to June 30 and while the com- pany also announced a special dividend this was not enough to prevent the FTSE 250 stock from falling 10 per cent or 30.3p to 264p.
Meanwhile, shares in online fashion retailer ASOS jumped 19 per cent on the back of continued speculation that it is in the takeover sights of an American firm.
It has been reported that Danish retailer Bestseller, which owns more than a quarter of ASOS, has been approached about selling its stake.
The biggest risers on the FTSE 100 Index were Petrofac up 26p to 1149p, Fresnillo up 16p to 928.5p, International Airlines Group up 5.5p to 363.6p and Morrisons up 2.6p to 184.4p.