By Steve Keating

RIO DE JANEIRO (Reuters) - Rio visitors have been warned of the risk of muggings during the Olympics but Senegal still could not avoid a brutal beat down as the U.S. women's basketball team began their bid for a sixth consecutive gold with a 121-56 rout on Sunday.

The result was as predictable as a tourist walking into one of the city's notorious favelas flashing a fistful of hundred dollar bills with Senegal searching for their first Olympic win going up against the all-conquering U.S., a true Olympic dynasty riding a 41-Games unbeaten run.

The 65-point margin of victory was the biggest ever in women's competition at an Olympics, bettering a 60-point win by the U.S. over Zaire at the 1996 Atlanta Olympics.

''You wait so long to play you're not quite sure what you are going to get, the kids were real anxious to play,'' said U.S. coach Geno Auriemma. ''They (Senegal) played hard and competed hard, obviously they are undermanned talent-wise when it comes to playing against the U.S. but you have to admire their effort.''

There were few witnesses to the crime, however, as the mismatch unfolded in a mostly empty Youth Arena.

Back in the Olympics for the first time since the 2000 Sydney Summer Games, where they went 0-5, Senegal had the few spectators in their corner, every basket bringing an enthusiastic cheer.

On cruise control from the opening tipoff, the U.S. never felt the need to shift into top gear, speeding to a 35-9 lead in the opening quarter and pulling away.

The U.S. benefits from a top-level college program that churns out basketball players in assembly-line fashion with the best moving on to play in the WNBA.

The system provides a talent pool no other country can match.

''They have a great group that has been together for awhile and that shows,'' said Senegal's Oumoui Thiam. ''We are here to learn, we are eager to learn. At the same time we are going to compete.

''The USA are world and Olympic champions for a reason but we gave it everything we got. It is an honor and something I will never forget.''

Along with immense skill, the U.S. also brings experience to Rio with nine of 12 players having already won gold medals, including co-captains Tamika Catchings, Diana Taurasi and Sue Bird, who have made it to the top of the podium three times.

All 12 members of the U.S. lineup hit the scoreboard, seven recording double figures led by 15-point efforts from Taurasi, Sylvia Fowles and Breanna Stewart.

''You never know how it is going to go exactly, obviously we were the heavy favorite,'' said Bird. ''Even though the Games have started and we are here and ready to go it is almost like a practice.

''With this game we were focused on ourselves.''

(Editing by Neil Robinson)