UPDATE 1-Mexico's Pemex posts $5.6 bln 3rd-qtr loss on lower output

(Adds details on output, sales)

MEXICO CITY, Oct 27 (Reuters) - Mexico's Pemex reported a narrower loss in the third quarter on Friday, but results for the state-run oil company were weighed down by a sharp slump in crude output.

The quarterly loss of 101.8 billion pesos ($5.6 billion) was about 14 percent lower than the 118 billion-peso figure the company posted in the same period last year.

The third-quarter loss broke a streak of three quarters in the black for the Mexican oil company.

Crude production averaged 1.884 million barrels per day (bpd), down nearly 12 percent compared with the July-September period last year and marking three consecutive months of output below 2 million bpd for the first time in decades.

Pemex attributed the fall to natural disasters that struck Mexico during the quarter, including storms and two major earthquakes in September that forced production at some facilities to shut down temporarily.

Sales during the quarter, however, grew 20.5 percent to 331 billion pesos due mostly to a recovery in prices, the company said in a filing with the Mexican stock exchange.

Prior to revising its fourth-quarter earnings report last year, which originally showed a loss, the company had suffered a five-year stretch of losses amid a dozen years of declining crude output and a global slump in oil prices since late 2014.

Pemex, officially Petroleos Mexicanos, lost its decades-long monopoly when Mexico implemented a constitutional energy reform in 2013.

Championed by President Enrique Pena Nieto, the reform also allowed Pemex to enter its first-ever joint ventures with equity partners in a bid to attract new capital and expertise in more complicated exploration and extraction projects. ($1 = 18.1785 Mexican pesos at end-Sept) (Reporting by Adriana Barrera and David Alire Garcia; Editing by Matthew Lewis)