Derry's Shane Duffy, whose father Brian hails from Letterkenny, opened the scoring for Martin O'Neill's side after just six minutes.
"It is an incredible feeling", said Eriksen.
The former Republic of Ireland global was highly critical of manager Martin O'Neill who selected a diamond formation against Denmark, a change from his defensive five-man midfield which played in Copenhagen on Saturday.
O'Neill said of his contract situation: "I haven't spoken to John since we talked about it, so I'll speak to John, I'm sure".
More poor play from Ward then set up Eriksen who blasted home his third goal of the game. "We were well beaten in the end".
O'Neill made two hurried substitutions at half time which completely tore apart his midfield, and instead of generating some pressure on Kasper Schmeichel's goal, it allowed Eriksen and Denmark more and more freedom. Everybody is entitled to a little bit of luck, so I totally disagree with you.
"He is one of the best players in the world but take that aside, as a guy and a person in the dressing room, he is a guy who can take the hopes of the nation on his shoulders and do magic with it".
Eriksen, who has scored 21 times in 75 internationals, said there were more goals to come from Denmark in Russian Federation.
Asked how far his free-flowing team could go at next year's tournament, Hareide said it would depend on the draw but added that the side wanted to improve and play good football.
"We tried to play, and we got the openings, and we got the goals".
After taking an early lead which sent spirits soaring inside a packed Aviva Stadium, Ireland were put down brutally by Denmark, for whom Eriksen was lethal after an untypical ineffectual display in the first leg. "That was the goal and aim before I started as the coach for Denmark and I am very pleased". It's a big thing and I'm very, very happy about it. We had to chase the game and Denmark took advantage.