PHOENIX ( Reuters ) - Wal-Mart Stores Inc ( WMT.N : Quote , Profile , Research , Stock Buzz ) plans to open its " Marketside " small-scale grocery stores in the Phoenix , Arizona area on October 4 , setting up a showdown with rival Tesco Plc ( TSCO.L : Quote , Profile , Research , Stock Buzz ) in the market for fresh groceries and prepared foods .