Tesco PLC (LSE:TSCO) and J Sainsbury PLC (LSE:SBRY) shares received a boost from Asda's latest trading update, with analysts arguing that the struggling supermarket group's continued market share losses underline the resilience of its larger listed rivals. Asda reported first-quarter like-for-like sales down 1.3%, an improvement on the 4.2% decline recorded in the previous quarter but still well short of the stabilisation many investors had hoped for.