Doha, May 7 Caster Semenya sent an Olympics warning to her rivals in Doha on Friday with a 2016 world best time in the 800m of 1:58.26, on a night otherwise dominated by Kenyan and American athletes. In the first Diamond League meeting of the season, Semanya powered through the final 200m and confirm her return to her very best form. In doubly bad news for her rivals in an Olympics year, the South African admitted afterwards she had held back from running at full pace during the race. Friday night’s time at the Qatar Sports Club stadium would have been good enough for her to finish sixth at the 2012 London Olympics. She seemed to labour through the first 500m and was well down the field as they approached the final bend. But then she eased past her rivals to secure first place. Ethiopia’s Habitam Alemu came second in a personal best time of 1:59.14 and Eunice Jepkoech Sum was third in 1:59.74, a season’s best for the Kenyan. Semenya said her early season form was down to “hard work” and running free of a knee injury which has plagued her for some time. The 25-year-old’s impressive victory came after an astonishing performance last month back home winning three races — the 400m, 800m and 1500m — in one afternoon. There she ran the 800m in 1:58.45. Semenya has been dogged by controversy since bursting onto the scene in the 2009 World Championships. Elsewhere, it was Kenyan middle-distance runners who impressed. In the men’s 1500m, three-time world champion Asbel Kiprop destroyed a high-class field to underline his stated intention to reclaim Olympic gold later this year.