Forward Thomas Muller said Bayern Munich were "too naive" as he and his manager both rued a number of missed chances in Wednesday's 2-1 home defeat to Real Madrid in the first leg of the Champions League semifinal.
Joshua Kimmich had put Bayern ahead in the first half but Marcelo equalised shortly before the break and Marco Asensio put the visitors ahead midway through the second half.
Muller and Robert Lewandowski both failed to convert close-range headers at the end of the first half, and Frank Ribery later saw two shots saved by Madrid keeper Keylor Navas, before Lewandowski pushed wide a gilded chance at a late equaliser.
"If you look at the whole game, we were too naive," Muller said. "We could not do what we have been doing the last few weeks, which is taking advantage of our chances.
"We could have had a much better result the way the game unfolded. The second goal was an individual error, the first one was weird, but ultimately we did not score our goals."
The scoreline after the first leg is the same as last year's quarterfinal between the two teams, when Bayern came back in the second leg in Madrid to force extra time, though Real eventually advanced to the next round and went on to lift the trophy.
"The result tonight could have been a lot different," Muller said. "We saw last year what is possible in Madrid, where we were able to turn around a 1-2 deficit.
"We had some very, very good chances, but maybe the importance of the game played a role. ... We went on to win 2-1 in Madrid last year [in 90 minutes] , but we should have got a much better result tonight."
Arjen Robben had to go off injured as early as the eighth minute, while central defender Jerome Boateng followed him down the tunnel with a groin injury in the 34th minute, while Heynckes also confirmed at a news conference that Javi Martinez also had to go off with concussion with 15 minutes remaining.
Heynckes said the German champions "didn't deserve to lose" and remained optimistic that his side can turn around the tie in the Bernabeu next Tuesday.
"After taking the lead, the game-changer was conceding a completely unnecessary goal right before half-time -- it was a gift for them, just like their second goal," Heynckes said.
"It's very rare to create so many chances in a Champions League semifinal but we didn't take them. Real Madrid don't normally allow so many opportunities but we weren't as efficient as we normally are and then we handed out those gifts.
"Of course, Real hold a big advantage but we didn't deserve to lose today, it was a game we should have won. That leaves me feeling a little optimistic.
"A semifinal is two games and we will try everything to try and turn the tie around in Madrid. That is the minimum requirement. We'll see where we stand after the second leg."
Bayern defender Niklas Sule referenced Liverpool's dominant performance in a 5-2 win over Roma in the other semifinal on Tuesday in expressing how many goal he thought his side should have scored.
"If we'd won 5-2 today, Real couldn't have had many complaints," he said.
ESPN's Bayern Munich correspondent Mark Lovell contributed to this report.