SAO PAULO, May 20 (Reuters) - Brazil's Ecorodovias SA won an auction on Friday to operate for 30 years the 727-kilometer highway system Rio-Valadares.

The highway operator, which was the only bidder, offered a 3.11% discount from the initial auction toll price, and is now expected to invest 11.3 billion reais ($2.32 billion) in the 30-year period. ($1 = 4.8698 reais) (Reporting by Alberto Alerigi Jr. and Peter Frontini; Editing by Chris Reese)