By Mitch Phillips RIO DE JANEIRO, Aug 18 (Reuters) - Alistair Brownlee won the Olympic triathlon in dominant style on Thursday, out-running brother Jonny in a British 1-2 to become the first to retain the title and underlining his position as the greatest-ever exponent of the swim-bike-run sport. Jonny, 26, third in London four years ago, went one better to take silver after being out-kicked by his 28-year-old brother in the heat of the concluding 10km run, with Henri Schoeman taking the bronze, South Africa's first medal in the sport since it was introduced in 2000. More...