Denmark beat Peru 1-0 in both sides' World Cup group stage opener on Saturday in Saransk.
Yussuf Poulsen made amends after conceding a first-half penalty that was awarded after the referee consulted the VAR system, but which Peru's midfielder Cueva
blasted over the crossbar.
"It was an emotional game, especially for me after giving away the penalty (...) I thought I was the bad guy, but then I was the good guy after scoring. That's the way soccer is," admitted the 24-year-old man-of-the-match.
Poulsen showed great finishing to hit the winner on 59 minutes to the dismay of the overwhelmingly Peruvian crowd in the 40,502-capacity stadium.
The win extends Denmark's unbeaten run to 16 games without defeat and ends Peru's 15-match unbeaten streak.
Peru's veteran Paolo Guerrero
, who only made it to Russia after a late reprieve for a ban, came on for the final 30 minutes, but his efforts at the Mordovia Arena came to no avail.
Denmark's goalkeeper Kasper Schmeichel played a key role with a string of second-half saves.
Authorities in Lima estimate around 25,000 fans flew to Russia to see their team's return to the World Cup and Saransk was a sea of Peruvian jerseys.
Their chants were near-deafening on occasion, as were the whistles each time Denmark had the ball or dared to attack.
"We were a little bit afraid of the atmosphere and the intensity of it, that affected us," admitted Hareide.
As a result, Peru dominated the opening 25 minutes, but after weathering the early storm, the Danes started to push forward.
They had to bring on Ajax's Lasse Schone with 36 minutes gone when central midfielder William Kvist was stretchered off with a suspected broken rib.
Hareide expects the midfielder to be ruled out of the rest of the tournament.
When Poulsen clipped Cueva's boot on 45 minutes, referee Bakary Gassama checked with the VAR.
He soon pointed to the spot for the second penalty awarded through the system of the day after France had also benefited against Australia.
Cueva took the spot-kick himself but, to Poulsen's relief, his effort ballooned over the bar.
Just moments after Peru wasted a clear chance when Cueva squared to Andre Carrillo who failed to connect, Denmark scored.
The ball was quickly moved forward and Poulsen showed great finishing to beat Gallese.
Guerrero was in the thick of Peru's bid to get level and his header fell into Schmeichel's arms five minutes later.
Tottenham midfielder Christian Eriksen, who netted 11 goals in qualifying for Denmark, had to busy himself in defense to snuff out Guerrero
With just over ten minutes left, Guerrero
again went agonizingly close when he pushed his shot past the post as Denmark held on.
"It was hard, we hope that in the course of the tournament things will go better," said Peru's forward Jefferson Farfan
"We didn't have the luck to convert our chances," he added.
With France having beaten Australia 2-1 in Kazan earlier Saturday, Denmark is placed second in Group C ahead of their next outing against Australia on Thursday with Peru facing the French.