Referee Bakary Gassama of Gambia went to the video after Cueva fell in the penalty box after an intervention from Denmark's Yurary Poulsen.
Denmark settled into the game after the interval and the talismanic Christian Eriksen provided Poulsen with a chance to turn his evening around in the 59th minute, and the 24-year-old made no mistake.
Orlando City midfielder Yoshi Yotun is expected to sit in the heart of Peru's midfield - a position he plays to great effect for the MLS side.
Gareca wouldn't commit to playing Guerrero against Denmark, but that didn't necessarily mean anything.
"Peru are an outstanding team", the Norwegian told reporters.
Making their return to the World Cup finals after a 36-year absence, the South Americans will provide a stern test for Age Hareide's Denmark side, and with France installed as Group C favourites, neither team will want to drop points at this early stage.
Some 26 years on from the final of Euro 1992, this was another performance by the Schmeichel family to savour.
Flores then scuffed an effort wide of the near post from close range on 57 minutes following good work by Cueva, who advanced into the area on the left and looked to set up Carrillo.More news: Oppressive humidity, heat continue Monday
Within his first two minutes on the field, his point-blank header was saved by Schmeichel.
Peru will be hoping to make up for last time as they compete in only their fifth World Cup and arrive on the back off a 15 game unbeaten streak, one of the best out of all the teams at the tournament.
Gareca added that Guerrero is "very, very fit", and "really is ready to play".
Peru deserved more. Their travelling fans deserved it too. Schmeichel turned away many by diving or extending whatever limb he could into the ball's path.
The Danish side that ended the Republic of Ireland's hopes of qualifying for the World Cup with a play-off victory last November needed some smart saves from keeper Kasper Schmeichel and desperate defending at times, but they navigated a route to victory with a 59th minute victor.
Although lacking in individual brilliance, Peru will be hoping their ability to adapt to different conditions serves them well in Russian Federation.
"While he is not the only player we have to concentrate on, I think facing players like him will allow us to grow and learn".
His connection was solid enough, but Scheimechel had the presence of mind to block the shot with his feet, practically tackling a team-mate in the process.
Right-back Henrik Dalsgaard, meanwhile, will become the first player under contract at Brentford to feature at a World Cup.