Real Sociedad captain Xabi Prieto lamented his side's missed chances after their 2-0 loss to Shakhtar Donetsk on Tuesday.
The La Liga outfit made a losing start to their UEFA Champions League campaign as Alex Teixeira's second-half brace led the Ukrainians to victory in the Group A clash in Spain.
Prieto said his team were punished for failing to take their opportunities as he rued their poor performance after the interval.
"In the first half we were the superior team but we didn't score and in the second we paid for that," the 30-year-old midfielder told reporters.
"In the second half the team fell apart and we paid for the way in which we played."
Real Sociedad coach Jagoba Arrasate agreed with midfielder Prieto and rued seeing Carlos Vela's 73rd-minute header strike the crossbar when his side were 1-0 down.
"We are left with a bitter taste in our mouths. We did enough to take the lead but after they scored they were highly efficient," Arrasate said.
"Yet, even then we could have equalised with that effort that came back off the crossbar. We were missing a killer instinct up front."
In a further blow, midfielder Esteban Granero, who is on loan from QPR, could be sidelined for an extended period after twisting his knee late in the clash.
"We are worried about the injury Esteban Granero picked up. His knee went," Arrasate said.
"We will wait for the results of the tests but it doesn't look good."
Real Sociedad will be looking to end their three-match winless run when they host Malaga in La Liga on Saturday.
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