WASHINGTON, Dec 11 (Reuters) - The U.S. trade deficit unexpectedly narrowed in September, touching the lowest level in more than five years, as exports accelerated and imports rose marginally, suggesting that trade likely provided a boost to economic growth in the third quarter. The trade gap contracted 10.9% to $52.8 billion, the lowest level since June 2020, the Commerce Department's Bureau of Economic Analysis and Census Bureau said on Thursday.