The Chelsea striker came off the bench after 90 goalless minutes in El Salvador and scored his side's winning goal, as they fought off a spirited American side inspired by Tim Howard's superb goalkeeping display.
|WORLD CUP SOCIAL HUB
|Keep up with all the latest news from Brazil and get involved in the debate on Twitter with our new World Cup Social Hub|
"The coach told me I was going to come on during extra-time," he explained.
"As soon as I got onto the pitch, I knew that I would find the net.
"From my very first sprint, there was a big chance. At that moment I was very happy, because for once I did something good on the pitch.
"I perhaps put myself under too much pressure. I just wanted the team to win and for us to continue.
"With the potential we have, if we had been knocked out today, we would have all been very disappointed.
"The bench has made the difference in recent games, which means everyone is contributing."
Belgium will face Argentina in the quarter-finals on Saturday.