The Chelsea forward, who played with Howard during his loan spell at Everton last season, came on at the start of extra time and made an instant impact as he played a hand in setting up Kevin De Bruyne's opener before scoring himself to give the Red Devils a 2-1 win.
Howard, who had kept the Americans in the contest with a series of excellent stops, breaking the record for the number of saves in a World Cup finals game with 15 in total, was full of praise for the 21-year-old's performance.
"They brought big Rom on and he was a handful," the Stars and Stripes shot stopper told Fifa's official website.
"He ran at us, scored a goal, created chances for other guys. Big Rom changed the game."
Despite going 2-0 down, USA forced a dramatic climax after teenager Julian Green's 107th-minute volley and Howard admitted that he was devastated that his team could not find a way to draw level.
"It's heartbreaking, I don't think we could have given any more," the 35-year-old continued.
"We left it all out there. We got beaten by a really good team. They took their chances well. It's heartache, it hurts. But hats off to Belgium, they were fantastic."