A day after the astonishing deeds of Usain Bolt and David Rudisha lifted the spirits of athletics fans the world over, the seedy underside of the sport was exposed on Friday as two former dopers won Olympic gold.
Asli Cakir Alptekin, who served a two-year ban for doping from 2004, led a Turkish 1-2 in the women's 1,500 metres, a race distance riddled with drugs in recent years.
Earlier, Russia's Tatyana Lysenko, who watched the 2008 Olympics on TV while serving a two-year doping ban, won the women's hammer with an Olympic record throw of 78.18 metres.
Also making an appearance in the men's 4x100m relay semi-finals were American Justin Gatlin and Briton Dwain Chambers, both time-served drugs cheats, and earlier in the day France and Kenya both confirmed pre-Games positive tests on distance runners Hassan Hirt and Mathew Kisorio.
Most of the 80,000 crowd lauding the superhuman successes in front of them on Friday will have had no idea that the gold medallists they were applauding had built their careers on illegal methods.
However, the hearty reception given to Chambers, a rarity among drug cheats in that he confessed, suggests they might have been in forgiving mood had they been informed.
Other athletes were not easily placated, however, and Briton Lisa Dobriskey spoke of her frustration after finishing 10th in the 1,500m.
"I'll probably get into trouble for saying this but I don't believe I'm competing on a level playing field'," she told the BBC.
Dobriskey, silver medallist in the 2009 world championships, said she thought the new blood passport system was proving effective and would weed out more dopers in the future but was clearly unhappy at having to share the track with one.
Her anger is understandable as barely a year passes without one of her rivals being exposed.
Moroccan Mariem Alaoui Selsouli, the world leader and favourite for 1,500m the London Games, tested positive in July and faces a lifetime ban having returned only last year from a two-year doping suspension for an EPO.
Also in July three Russian runners, including major championship middle-distance medallists Svetlana Klyuka and Yevgenia Zinurova, were banned while four years ago no fewer than seven Russians were caught in one hit.
That heavyweight haul included then-world leader and former indoor 1,500m world record holder Yelena Soboleva and former double world champion Tatyana Tomashova.
There was some good news for fans of "clean sport" on Friday, though, as one of the oldest and most discredited world records on the books was finally displaced.
The United States won the women's 4x100 metres relay in 40.82 seconds to erase the 41.37 set by East Germany in 1985.
None of Silke Gladisch-Moeller, Sabine Rieger, Ingrid Auerswald-Lange and Marlies Goehr were caught by the relative primitive drug tests of the time but after evidence of systematic doping in the country subsequently emerged, their record was treated with scepticism and derision.