Steve McClaren admitted Middlesbrough's luck finally ran out in the UEFA Cup final.
Boro staged two epic fightbacks from three goals down to make it to the final in Eindhoven.
But they were torn apart by Sevilla, who scored three times in the last 12 minutes to win 4-0.
McClaren said: 'I don't know if the occasion got to our players. We looked nervous. There was no freedom and we didn't perform as we can.
'We had three goalscoring chances for an equaliser and a stone-wall penalty.
'It could have changed the game but, as it was, our luck ran out.'
Middlesbrough wanted a penalty when Javi Navarro barged into the back of Mark Viduka, two minutes before Sevilla's second, but their appeals were ignored.
Boro went behind midway through the first half to a header from Luis Fabiano.
Enzo Maresca added two more and former Spurs striker Frederic Kanoute grabbed the fourth in the dying minutes.
McClaren, who will become England manager after the World Cup, said: 'It's the finale of my Middlesbrough career.
'It ends on a bad night but I will reflect on it. I have left them in good condition and go on.
'I have enjoyed my five years and am sad to go, but people move on in football. I will go with my head held high.
'I don't like losing football matches and I didn't think they were four goals better than us on the night. We didn't perform as we can but I am so proud of the run and our experiences in Europe have been fantastic.'
The departing manager urged his players to build a bright new era for the club from the ashes of this defeat.
It is the heaviest loss suffered in the UEFA Cup final since it changed from two legs to a one-off game.
But Boro can look back on an incredible journey and the miraculous comebacks against Basel and Steaua Bucharest.
McClaren said: 'This is the club's reward, getting to the final, but it doesn't stop there and that's what I've told the players.
'I've said this is just the beginning. It is a stepping-stone, a platform to achieve more.
'They have the backing of a tremendous chairman, the resources and the talent coming through to compete at this level.
'The club must take it forward. They must not let this be the end. It must be a new beginning.'
Asked whether his move to England had distracted the team, McClaren said: 'We've dealt with it in the past and dealt with it well. Sevilla were better than us on the night.'