There were tears before the game - Lukaku dedicates performance to Eriksen
Eriksen collapsed on the pitch earlier on Saturday when Denmark took on Finland and received emergency treatment in worrying scenes that caused the suspension of the match.
But he is now awake and stable and the match was completed after discussions between both teams.
Belgium v Russia also went ahead in Saint Petersburg, with Lukaku scoring twice in a 3-0 win as his team made an impressive start to the tournament.
But despite his star showing, Lukaku found it tough to take part in the match after what he had watched with Eriksen, who was still central to his thoughts as he reflected on the victory.
"There were a lot of tears before the game," Lukaku told reporters after the match.
"It was very difficult to focus for this match, also for Toby [Alderweireld], Jan [Vertonghen], Nacer [Chadli].
"We all know him very well. I hope he gets well again; he has two young children, they need him and so do we as a team. I’m happy with the win but my thoughts are with Christian now."
Lukaku: It was difficult to play
Lukaku ran to a TV camera and said "Chris, I love you" in support of Eriksen after netting his first goal.
He later added to beIN SPORTS: "It was difficult to play because my mind was with my team-mate, Christian.
"I hope he is healthy and I dedicate this performance to him.
"I cried a lot because I was scared, obviously. We lived strong moments together for a year and a half. I spent more time with him than with my family.
"My thoughts are with him, his girlfriend, his two kids and his family."
There were similar sentiments from Alderweireld after the match on social media, as support for Eriksen flooded in from all those connected with football.
Lukaku's Belgium and Denmark will play in Copenhagen on Thursday.