Waitrose's turnover has rocketed 10 per cent since it bought 19 former Safeway stores from Morrisons in March.
Latest TNS market share figures showed Waitrose's sales rose to£527 million for the 12 weeks to August 15, compared with£479 million for the same period last year.
Its share rose from 3 per cent to 3.2 per cent over the 12-week period.
However, Tesco's share was 28.1 per cent, compared with 26.8 per cent the previous year. TNS Superpanel communications director Edward Garner said: 'In terms of straight cash growth year on year, Tesco dominates, adding more than two and a half times the turnover gained by the Morrisons fascia.'
Asda's share stood at 16.6 per cent, Sainsbury's at 15.4 per cent and Morrisons/Safeway at 13.9 per cent.