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 will be looking to end their three-match winless run when they host Malaga in La Liga on Saturday.
‘The pure simplicity of the way Slot has managed the squad is probably the biggest thing I could say about him. It’s not broken, so let’s get on with it’: Liverpool legend full of admiration for Jurgen Klopp's successor at Anfield
‘I trained at Spurs and thought they’d give me a chance. But I received a letter thanking me but saying they didn’t think I was good enough – I was gutted’: How Tottenham missed out on signing Wales legend John Toshack
