UPDATE 2-Mexico's Walmex Jan. same-store sales up 5.5 pct

* Jan same-store sales rise 5.5 pct, beat forecast

* Additional Sunday lifts results

* Robust traffic, but ticket remains weak (Adds Aurrera format, background)

MEXICO CITY, Feb 5 (Reuters) - Mexico's top retailer, Wal-Mart de Mexico posted on Friday a 5.5 percent increase in January same-store sales, exceeding analysts' expectations by nearly a percentage point.

The company, known as Walmex (WALMEXV.MX), got a lift from an additional Sunday in January this year compared with the same month of 2009, when same-store sales, or those recorded at stores that have been open for at least 12 months, rose 2.7 percent.

Walmex is 68.5 percent owned by U.S. retailer Wal-Mart Stores (WMT.N).

Further discounts on staple foods during the first month of 2010 attracted more visitors to Walmex's stores. Same-store traffic rose 6.1 percent in January, but the average ticket, or money spent on every visit, slipped 0.5 percent.

As customers were slapped with higher taxes and fuel prices during January, Walmex cut prices on 1,000 staple foods at its flagship Walmart stores. It also introduced an array of 10 peso (77 cent) products at its Aurrera format, no-frills, warehouse-like stores aimed at low-income shoppers.

Mexican retailers struggled last year because of the recession.

The company is due to file its fourth-quarter results next week.

Walmex recently bought 519 stores in Central America from its parent. Shares fell 1.39 percent to 55.96 pesos before the company announced it January sales. (Reporting by Cyntia Barrera Diaz)