NEW YORK – McDonald's Corp. is having trouble stomaching the competition.

The world's biggest hamburger chain said Thursday that a key sales figure fell for the first time in nearly a decade in October, as it faced intensifying competition and a challenging economy. The company, based in Oak Brook, Ill., says global revenue at restaurants open at least 13 months fell 1.8 percent for the month. The last time it dropped was in March 2003.

The figure is a key metric because it strips out the impact of newly opened and closed locations. It's a snapshot of money spent on food at both company-owned and franchised restaurants and does not reflect corporate revenue.