Belgium victory took a toll
It often happens in sport that a team produce a brilliant performance and then pay the price in their next game.
Wales matched Portugal in the first half but after the break you could see the effect that their extraordinary efforts in beating Belgium 3-1 were having on them.
The amount that they put into that famous victory in the quarter-final took an awful lot out of them.
Joe Allen, for example, is a far better player than he showed on Wednesday, when he found it hard going.
Portugal's strong points
Much has been made of Wales' fine organisation, and rightly so, but Portugal have also been one of the best teams defensively in the tournament, aside from that strange 3-3 draw with Hungary.
They rely on counter-attacks, on the speed of Ronaldo and Nani; they don't overcommit when pushing forward and as soon as they lose the ball they get back very quickly.
There was much talk before the match about how Portugal had not won a game in 90 minutes at Euro 2016 but they hadn't lost a match either.
Ronaldo leaps to conquer
Heading is an art form and Ronaldo is a master. It's all in the timing really.
You have to know exactly when to jump so that you will be at maximum height when the ball arrives, and then you have to make contact at precisely the right time to exert power, as he showed.
He has also worked very hard on his thighs, which are enormous for his frame, and that helps his spring. It's remarkable: He came into football as a winger and has developed into a Nat Lofthouse (who has one of the greatest goals-per-game ratios of any player to represent England ).
Collins played his role well
James Collins had only played for a couple of minutes at Euro 2016 before Wednesday but he was able to impose himself straight away at centre-back.
Portugal were regularly chipping the ball into the penalty area for Ronaldo, but Collins stuck tight to him.
However, Ronaldo climbed above James Chester late in the first half to send a far-post header over the crossbar, and he beat the same player in the air to give Portugal the lead five minutes after the interval.
THE TIMES, LONDON