Swansea manager Brendan Rodgers revealed conceding two goals enabled his team to "refocus" and make sure of promotion to the Premier League.
Press Pass: Swansea promoted
The Swans led 3-0 but two goals in the early stages of the second half brought Reading back into it - only for Scott Sinclair to complete his hat-trick and wrap up a 4-2 success with a second penalty.
Rodgers, who managed Reading himself in 2009, told Sky Sports after the Wembley contest: "It was a fantastic game.
"I don't think we played as well as we did for most of the season but on the moments when we did show our quality we were very, very good. Conceding two goals helped us refocus and get a bit of control."
Rodgers continued: "It's fantastic. The supporters today were incredible and it's nice to repay their faith and get promotion.
"It was a proper, proper game and these players deserve to be in the Premier League. Ourselves, Norwich and QPR will be a credit to the Championship and will try to do well.
"We show courage and try to pass the ball - but the important thing today was to try to win the game. I said to the players it wasn't about winning, it was about defending our principles and how we played.
"We got a bit nervy but regained our composure and started to pass the ball."
Next month the 38-year-old will climb Mount Kilimanjaro for charity, after the death of his mother Christina, and he added: "That will be a different challenge."
Hat-trick hero Sinclair, on-loan from Chelsea, continued: "I'm buzzing. Credit to the boys - it's fantastic.
"Brendan deserves massive credit - he's been exceptional and puts all the hard work in every day in training."
Stephen Dobbie, scorer of Swansea's third goal, said: "We knew Reading would come out and make it a fantastic second half.
"To be a part of this team, to make history and for a team from Wales to be in the Premier League is an honour."
The Swansea players wore T-shirts with Besian Idrizaj on as they celebrated victory - and Nathan Dyer and Garry Monk were keen to remember their former team-mate, who died a year ago of a heart attack at the age of 22.
Dyer said: "He's always in our memories."
Monk added: "It's for Besian. What a day. We've worked so hard all season. I wish Reading could go up with us - they've been fantastic all season too.
"We never do anything easy but we saw it out. It's unbelievable. A lot of people have been doubting us for a long time so it's nice to put them right. We play football the right way."
Reflecting on the threat of relegation which hovered over the club less than a decade ago, long-serving midfielder Leon Britton said: "It's an unbelievable story to be in the Premier League eight years down the line from being on the verge of going out of the Football League.
"Paulo Sousa started it off - give him credit - and Brendan has been fantastic. Getting Swansea to the Premier League is an outstanding achievement."
Club chairman Huw Jenkins said he was still coming to terms with what the team had achieved.
"Travelling back I think we will have to pinch ourselves to get back to reality," he told Sky Sports. "It's been a remarkable 10 years for this club and to have an opportunity to continue growing and building next year - and playing the very best teams in the country - is fantastic.
"We had our luck today and sometimes in sport you need that but I think it's a great achievement - not too many teams play this way in Britain. We've stuck with it through different managers and we want to continue that path next year. Hopefully that philosophy will continue for a long time.
"Go back two years and we thought we had a massive task when we got into the Championship - so we've got no worries going in and testing ourselves against the best. We'll give it everything we've got.''
McDermott congratulated Swansea on their achievement and said his Reading team could still be proud of their season despite the defeat.
"In February we were 12th or 13th but we've got into the play-offs and beaten Cardiff to come to Wembley. In the first half nothing dropped for us but Swansea played very well. 3-0 down is a mountain to climb but we were inches from getting a third goal.
"Jem Karacan hit the post and if it had gone in I think we'd have gone on to win the game...I honestly believe it would have been a different scoreline. I'm just really disappointed for our fans. I wish we could have got the right result for them."