Jorge Carlos Martins fired thePortuguese ahead on the stroke of half-time before second-half goalsfrom Helder Postiga, Spain defender Sergio Ramos, who put through hisown goal, and substitute Hugo Almeida sealed a deserved win for thehosts.
Carlos Martins, second right, celebrates after scoring Portugal's opening goal
The victory allowed Portugal to gain a measure of revenge for their World Cup exit at the hands of the Spanish, having lost 1-0 at the last-16 stage, and saw new coach Paulo Bento earn his third successive win since he replaced Carlos Queiroz in September.
For Spain, it was the second heavy friendly defeat in the space of two months following their 4-1 loss against Argentina, and Fabregas, who replaced Xavi at half-time, admits it was a night to forget.
'We're hurt. It's been a big scoreline but we have to lift ourselves. We wanted to finish the year well but now we have to wait until February,' the Arsenal playmaker told Spanish television channel TVE.'It's not been our best game but you also have to know how to lose.
Show off: Portugal's Cristiano Ronaldo, left, dribbles past Spain's Sergio Ramos
'The truth is it's a match where we can't take anything positive. They played better than us, they had a lot of desire'
Fabregas. who also feels that manyof the Spain squad are still trying to get back to peak fitnessfollowing their heroics in South Africa this summer, added: 'Now weneed to apologise to the fans and continue forward.'
Not very friendly: Ref Antony Gaultier shows Spain's Cesc Fabregas a yellow card for a foul on Portugal's Pepe
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Explore more:People: Sergio Ramos, Xavi, Carlos Queiroz Places: Lisbon, Spain, Argentina, Portugal, South Africa