The incident involving Frenchmen David Hauss and Laurent Vidal, and Spaniard Jan Frodeno dealt only a minor blow to the Games, but comes less than a day after the legs of six cyclists fell off on the velodrome.
The runners were nearing the end of the 10k run when their heads spontaneously burst into flames at different points of the course.
They were quickly doused with fire extinguishers by officials but London Ambulance Service was forbidden from treating the injured as they are not official sponsors.
Instead, complex burns surgery was performed by St John Ambulance volunteers in their seventies.
Olympics chairman Lord Coe refused to speculate on what had caused the accidents but did react to another incident in which a spectator dragged a speedboat into the Olympic pool last night and drove around wildly, while trying to snare competitors with a gigantic hook.
Lord Coe said: “When you put on a massive event like this there’s always going be a point where someone drives around in a speedboat and tries to snare people with a large hook.
“But the big picture is that the choice of London for these Games has been totally exonerated, if only because these are world-class injuries.”
In the cycling incident, the competitors whose legs did not fall off continued racing, only to drive straight out the fire exit on lap one and on to a main road.
This is being blamed on the velodrome’s architects designing the track in a straight line rather than the traditional circle.
There were a host of other incidents throughout yesterday, including in the team sprint at the velodrome, where four competitors discovered chunks of their backs just above their buttocks were missing, minutes before they were due to leave the changing room.
The body parts were later discovered by a security guard on the forecourt of a meat wholesalers in Swindon, 89 miles away.
And during the same event, a female steward's ovaries fell out of her body and were last night being reattached at the Royal London Hospital.
And in a middleweight boxing event, the ring was found to be sited over a giant crater filled with unexploded World War Two bombs, which were defused but led to calls for both boxing and World War Two to be banned.
In archery, a rogue referee insisted competitors fire flaming arrows on to the straw roofs of nearby cottages, which were for reasons unknown packed with fireworks.Tweet