Space faring human race encounters one highly advanced spaceship. The one ship tells the human space fleet to go away and leave them alone. We don't listen and our ships are destroyed. Human spy is sent to the alien world. Aliens look virtually identical to humans except they have no cartilage in their nose and the 'females' are only capable of mating every seven years. The human spy tells this story and is a brilliant tactician. He enters into a game tournament where they play a very complicated version of chess. Human spy interacts with a higher ranking military officer who has a human female wife. Human spy gets caught and when he is ultimately returned to Earth he advises humanity to unconditionally surrender to the alien race. Humans eventually win because the alien males take human wives and their alien DNA is diluted in the vast human gene pool.
Looking for the title and author if anyone can recall them.
06/15 - update
I found the anthology. 'Second Game' was in 'The Arbor House Treasury of Great Science Fiction Short Novels' which came out in 1980 and 1981. I did read the original story from 1958 which was actually a nominee for the Hugo Award for Novelette in 1959.