Russia coach Stanislav Cherchesov was disappointed after his team conceded all three goals in their 3-0 World Cup Group A loss to Uruguay from set-pieces.
After an early Luis Suarez free kick, Russia gave away two goals from corners as the hosts failed to secure top spot in Group A.
"When you commit errors, I believe you give an opportunity to your opponent," Cherchesov told reporters.
"In our training sessions we played against these set pieces, and today our opponents scored from set pieces. We wanted to stop this but we could not succeed."
Cherchesov also criticised his players for not being well prepared mentally.
"Training sessions are one thing and then on the pitch is another thing. It is an art to be prepared and not just think you are prepared," he added.
"We were not very successful at this in the beginning and we need to not be as relaxed as we were today."
Cherchesov said he could still take positives from the match into Russia's round-of-16 game against the Group B winners, either Spain, Portugal or Iran.
"I said already that Uruguay has top-notch players. We have good players too, some are better than theirs," the coach said.
"I am pleased with my players as, after we lost a player [full-back Igor Smolnikov, sent off for two bookings], we were aggressive and showed we were real men."
Cherchesov said he was looking forward to the next game at Moscow's Luzhniki Stadium, where Russia play the majority of their matches.
"Luzhniki Stadium is my stadium. I love it," he said. "We do not have the word problem in our vocabulary. Everybody is ready."