Swansea manager Brendan Rodgers revealed conceding two goals enabled his team to "refocus" and make sure of promotion to the Barclays Premier League.
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 - it's fantastic."
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 (runners-up) Norwich and (champions) 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 other 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."