UPDATE 1-Mexico's Walmex Oct same-store sales down 0.9 pct

MEXICO CITY Nov 8 (Reuters) - Mexico's biggest retailer, Wal-Mart de Mexico, said on Thursday that sales at its Mexican stores open for at least a year slipped 0.9 percent in October from a year ago, its first monthly decline in 19 months.

Results were a tad below expectations of a 1 percent decline in a Reuters survey of six sector analysts.

Last month had a weekend less than October of 2011, eliminating two important shopping days from the retailer's calendar.

Walmex , an affiliate of top global retailer Wal-Mart Stores Inc, said it operated 2,224 stores in Mexico and 633 in Central America at the end of September.