Tesco returned to growth for the first time in a year, according to fresh data from Kantar Worldpanel, but lost market share as the sector grew as a whole, with Sainsbury losing its position as the second largest retailer by market share to Asda.The price war between supermarkets that has now seen a 17th successive monthly fall in prices, helped the grocery market accelerate to its fastest rate of sales growth since last June, up 1.1% in the 12 weeks to 1 February.Tesco grew sales 0.3% in the period but saw its market share shrink further, as discounters Aldi and Lidl continued to take a bigger piece of the pie."Britain's largest retailer is bouncing back from a tough year, with Dave Lewis's efforts to overhaul the supermarket attracting an additional 236,000 shoppers into its stores in the last 12 weeks," said Fraser McKevitt, head of retail and consumer insight at Kantar."Despite the increase in sales, Tesco's overall market share fell to 29.0%, down by 0.2 percentage points compared to last year."McKevitt said shoppers took advantage of a like-for-like fall in grocery prices of 1.2%, another record low that amounted to a saving for Britain's shoppers of £327m over the period.He said the market's 1.1% growth is low by historical standards "but a considerable improvement compared to November 2014, when the market contracted".Asda overtakes Sainsbury's as number-twoAsda grew its market share to 16.9%, overtaking Sainsbury's, which traditionally performs more strongly at Christmas than the rest of the year.Both Asda and Sainsbury's suffered declines in sales compared with a year ago - Asda by 1.7% and Sainsbury's by 1.0%.Morrisons enjoyed its best performance since December 2013 as sales fell by 0.4%, though this was not enough to save chief executive Dalton Philips.Discounters face tougher timeAldi and Lidl grew their market shares by 0.8 and 0.4 percentage points, respectively, to 4.9% and 3.5%.Aldi's strong growth of 21.2% slowed from its 36% peak in May 2014, with Lidl's 14.2% growth down from its maximum of 24%.Said McKevitt: "Early results suggest that discounters Aldi and Lidl will find their accelerated growth levels hard to match in 2015."