Australia lost the Ashes outright for a third successive time, but the first under Clarke's leadership, when they were bowled out for 224 to go down by 74 runs tonight in the fourth Investec Test at Chester-le-Street.
After Stuart Broad had proved too much for the tourists to handle - including Clarke, who was bowled by an especially good delivery - the Australia captain reflected on a 3-0 scoreline, with just the final Test to come at The Oval.
"A lot of things are hard to swallow at the moment," he said.
"Obviously our middle order find different ways to get out, which is extremely disappointing.
"But I have to pay credit to Stuart Broad. I think his performance was exceptional."
Broad (six for 50) finished with 11 wickets in the match as Australia lost their last eight for 56 runs, and nine in an extended final session.
"It's extremely disappointing - I guess I know now what it feels like to lose an Ashes series as a captain," said Clarke.
"The most difficult thing to take is that our preparation and training has been excellent - I can't ask for anything more from our players in regards to preparation.
"At the moment, we are being outplayed."
As for his own dismissal, he added: "It was a good ball, but the great batsmen find ways to keep those out.
"You see that in good bowlers all the time - it's about finding a way to combat that and get through that spell and still be batting at the other side.
"But unfortunately, in both innings we couldn't get through it."
Clarke does not accept his team, who have lost seven out of their last eight Tests, no longer know how to come out on top.
"I don't think today was about forgetting how to win," he insisted.
"I just think a good bowler got his back up and got momentum with it, and we couldn't stop him."
Clarke insists the buck stops with him, not just as captain but as a key batsman.
He piled up 187 in the first innings of the drawn third Test in Manchester, but said: "My job is first and foremost to score runs, and I only made 25 in this Test. That's unacceptable.
"When you pick the squad you have to keep the faith and try and get the best out of them - and it would be nice if the captain led by example and scored a few more runs as well."