Hearts manager Craig Levein was left to rue "two body blows" after his side were swept aside by Celtic in the second half of their Scottish League Cup semi-final.
The concession of what Levein called a "very soft" penalty led to Scott Sinclair's opener.
And a mistake by goalkeeper Zdenek Zlamal led to Celtic's second as they went on to win 3-0.
"We never got to play to our potential, which was frustrating," said Levein.
"The two body blows we got were in a small way down to ourselves so we have to take that on the chin.
"We had a similar situation at Ibrox a few weeks ago [the 3-1 defeat] where we were looking forward to the game and thinking we've got a chance of winning and then contribute to our own downfall."
Peter Haring returned to the Hearts team, having missed the last two matches with a hernia problem.
But Levein revealed the Austrian was struggling again by half-time, and despite going on to play the full 90 minutes, is now "back to square one".
Haring will miss at least Wednesday's Premiership derby with Hibernian, as will top scorer Steven Naismith, who lasted just eight minutes before succumbing to a knee injury that will likely sideline him "for at least a couple of games".
Celtic edged ahead in the early stages of the second half through Sinclair's spot-kick and, from then on, the holders dominated, with Zlamal spilling the ball in the run-up to James Forrest's goal and Ryan Christie lashing in a third.
"I was just at that point where I felt Celtic were getting disappointed and looked a little bit leggy," Levein told BBC Radio Scotland's Sportsound.
"I was extremely happy with the way things had worked out. They didn't seem to be able to cause us any problems.
"And then, of course, the penalty situation arises and gives them a massive lift and disappoints our players. It changed the feeling of the game."
Hearts keeper Zlamal later apologised for the blunder that helped put Celtic 2-0 ahead.
"The second goal was mine. I think Michael Smith touched it a little bit but I have to catch it," he said. "I have to say sorry to all the fans and to everybody.
"Mistakes are part of football. It's normal, everybody makes mistakes. I was focused on trying not to concede another goal. But Celtic were much better than us after the second goal."
'Hearts were blown away' - analysis
Scotland assistant manager James McFadden on Sportsound
Having watched it back, I would say it's a penalty. Not a blatant penalty, but Bozanic catches Christie just above the knee.
The Steven Naismith injury is probably the pivotal moment. He's a leader, he leads by example, he organises, he tells people where to be, he can manage the game.
At times in the game where they needed to get control and regroup, he'd have been the one to do that. It was a blow for Hearts and gave Celtic a lift, knowing the guy going off is probably the form player in the country and the man who makes Hearts tick.