Sebastian Coe has hailed Mo Farah's double Olympic gold as an achievement of "extraordinary magnitude".
Farah completed the long-distance double with a scintillating display in the 5,000 metres last night, one week after topping the podium in the 10,000m.
It puts him in esteemed company in distance running as one of just six athletes who have won both events at the same Games, and Coe was emphatic in his praise.
"What Mo did last night was of such an extraordinary magnitude," he told Radio 5 Live.
"The real challenge of doing the double is not actually the physicality of going through rounds and races, it's those three to four days between having won an Olympic title and then deciding it's still important enough in your life to come back on to the track and do it all over again.
"It's probably tougher mentally than physically."
While some questioned if Farah could produce the goods for a second time following his exertions in the 10,000m and the heats of the 5,000m, Coe had little doubt he would see the Briton with another medal around his neck.
"There is a moment in a career of an athlete when they're just not going to get beaten," he added. "You're very lucky if you hold that period for 18 months - John Walker had it, Steve Ovett had it, Steve Cram had it - all the great athletes have it.
"Mo is in that period now. I think he goes into races genuinely believing he's going to win. The reverse of that means the rest of the field - whether they admit it publicly or even in their quieter moments - think they're running for second place."