Day captained his country for the first time in the final pool match against the USA in La Roche-Sur-Yon, leading from the front by scoring England Under-20's first individual hat trick since 2012.
"It was a massive win," Day told the RFU Podcast. "It was obviously a very proud moment for myself to captain the side, but first and foremost we had to get the win.
"It's always nice to get a few tries, but as I say, I'm more than happy just to get the win and progress to the semi-finals.
"I don't think that the scoreline reflected the fight that the USA put up. So credit to our boys, who stuck at it for 80 minutes."
England got on the scoreboard with just 26 seconds on the clock, and continued crossing the whitewash until the 74th minute, racking up a Junior World Championship record score in the process.
Keeping the scoreboard ticking over proved crucial as England reached the semi-finals on points difference ahead of Ireland, and the Harwich-born youngster said that the achievement was reached because the players concentrated on what they were doing and not on what was going on elsewhere.
"We weren't focused on what other teams were doing, we were only concentrating on scoring as many points as we could against the USA," he commented. "We stuck at it for the whole 80 and managed to get a decent scoreline which thankfully pushed us through to the semi-finals."
Day's hat trick may have grabbed the headlines, but two of his club mates also helped ensure that more points went to Saints representatives than any other club. Centre Tom Stephenson crossed the whitewash twice, with fly half Will Hooley landing 11 conversions.
"Both Will and Tom played really well," the scrum-half said. "It's a credit to Saints and the Academy and what they're going with the boys and how they're pushing the talent through. I'm really happy for those two, and to go through the full 80 as well."
Having earned their way out of the pool stages with two wins from their three matches, England face New Zealand in next Tuesday's semi-final.
Day is under no illusions as to the challenge that will be posed by the Baby Blacks, who won the Junior World Championships four successive times between 2008 and 2011, and who were the losing finalists 12 months ago.
"You've got to play the best to win a tournament like this," he said. "New Zealand are traditionally the best in the world, and all the boys are looking forward to playing them. We're going to have to up our game another level and it'll be a good test."