Eddie Howe's side netted all four goals before half-time as Sean Longstaff's brace, either side of impressive finishes from Jacob Murphy and Anthony Gordon, sent the hosts into a commanding lead before the break.
Miley, who played 63 minutes of the friendly encounter against the La Liga outfit, reflected positively on his maiden start for his boyhood club on home soil.
The Stanley-born youngster, who joined Newcastle's Academy in 2014, told newcastleunited.com: "It couldn't have gone any better! I've been on the bench a few times but never got on so it was great to be in from the start, something I've always dreamt of.
"I just got a text yesterday and after doing the walkthroughs this morning, I found out I was in the starting XI so it took me a bit by surprise. I didn't have much time to think about it which is sometimes the best way, to go straight into it, and all the lads were brilliant with me. They led by example and I followed."
"The start to the game was really positive. For me to be a part of that was even better and I think the gaffer will be pleased with the way we pressed and the goals we scored was a rewarding thing that we wanted.
"I thought I did well. It's always a bit nervy when you haven't been around the team as much but, once I was on the pitch, I was fine and the lads were encouraging me all the time."
Miley, older brother of Lewis, made his full senior debut during Newcastle's 2-0 away win against Hull City a fortnight ago and has relished his pre-season involvement with the Magpies' first-team, recording two assists in the process.
The 20-year-old is hopeful of building on his bright displays in the middle of the park in recent weeks and also expressed his joy in playing in front of over 31,000 home supporters.
"It has been a great pre-season for me," Miley added. "I've played a lot of minutes for the first-team and the main aim is to stay around it. You saw it with Lewis last season and if I keep doing what the gaffer asks of me, building that trust with him, then who knows where I could go.
"Watching my brother from the stands last year to now being in the position that he's been in last season is really nice. You don't realise when you're out on the pitch but when you come off, it hits you.
"It was excellent to play in front of that many people. The Toon fans are always the best they can be. When I was in the game, it was a bit different and you don't feel it as much but when you come off and you're walking around to give the appreciation they deserve, it's really nice."
