Red-faced and straight from the United dressing room, Ferguson admitted that Barcelona had been the better team, but seemed to accept that his side could have done better.
Hitting out: Sir Alex Ferguson snapped at a reporter
Clarke followed up, not unreasonably, with the obvious question. 'In what areas did you expect to do better?' he asked.
It was, as millions of viewers were to discover, the straw that broke the camel's back.
'That's all I'm saying, right?' Ferguson fired back, as the atmosphere turned glacial.
Like a boxer caught with a shot he simply never saw coming, Clarke reeled back, tried to compose himself and tried a different tack.
Contrasting fortunes: Rooney leaves the pitch dejected as Barcelona celebrate a famous win
He threw out a flurry of olive branches - called him 'Alex', risked a sympathetic shrug and asked about Edwin van der Sar and Paul Scholes - but the damage had been done.
Eventually, Clarke was reduced to trying to end the painful encounter on a positive note. 'Thanks for joining us,' he said. 'Right. OK,' came the reply, as Ferguson marched off, without a backwards glance.
United had spent 90 minutes wondering where the next blow was going to come from and trying to anticipate the unexpected. In 90 excruciating seconds, Gabriel Clarke came to understand precisely how they felt.
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Explore more:People: Paul Scholes, Alex Ferguson, Edwin Van Der Sar Places: Barcelona