Grocery inflation was 2.9 percent during the period, down from 3.6 percent in Kantar's February report.
Market researcher Kantar Worldpanel said Tesco and Morrisons' sales both increased 2.7 percent year-on-year over the 12 weeks to February 25 - ahead of growth of 2.3 percent at No. 3 Asda and 1.1 percent at No. 2 Sainsbury's.
The big four's growth continued to be outpaced by discounters Aldi and Lidl, whose sales were up 13.9 percent and 13.3 percent respectively.
(Reporting by James Davey; editing by Kate Holton)