A chastened Oscar Pistorius moved Monday to defuse the row that threatens to blemish the clean-cut image he forged during a protracted struggle to compete alongside able-bodied rivals.

For years Pistorius was the poster boy of the Paralympics. But the era of invincibility for the so-called ‘‘Blade Runner’’ appeared to end when his bid for a third straight gold in the 200 meters was thwarted Sunday night in London by another double amputee on carbon fiber prosthesis. Alan Oliveira of Brazil came storming down the home straight to overtake the defending champion.

Rather than hailing his rival, Pistorius accused Oliveira of gaining an unfair edge by using lengthened blades. That’s despite spending years himself convincing authorities he should be allowed to compete in the Olympics — a feat he achieved last month — because his prosthesis did not influence his athletic capabilities.

To many, the South African sounded like a sore loser.

‘‘I would never want to detract from another athlete’s moment of triumph,’’ he said in a statement Monday. ‘‘And I want to apologize for the timing of my comments.’’

AP