Luis Milla's men struggled with the Japan's aggressive tactics throughout and never recovered from going down to ten men when Inigo Martinez was sent-off for denying a clear goalscoring opportunity four minutes before half-time.
But Romeu believes the Olympic team can learn from the Spanish senior side that lost their first match of the 2010 FIFA World Cup™ to Switzerland before going on to win the competition. He told the Spanish Football Federation's website: "The first game wasn't as good as we had hoped but this is football.
"Many national teams have won World Cups and European Championships having not won the first game, it is not how you start but how you finish."
"In the dressing room after the defeat everyone was encouraging each other to move forward. This is a good thing to have in difficult moments, it comes from inside of us and I think we will show our resolve in the two games left in the group stages and those that come afterwards.
"We are the ones who believe in ourselves most, we have strength and desire and we are sure we are going to do something great."
The Chelsea man is also determined to put the disappointment of yesterday's result behind him to enjoy the opening ceremony which takes place in London this evening.
"For me it creates a special excitement because this is the city I have been living in for the past year and I hope I will be living in for many more," he said. "I am at home and to live such an amazing event is very lucky. We expect to enjoy it."