It is certainly the biggest game in the history of Welsh football, while some will be wondering just how Portugal have got to this stage of the competition, but one of them will be playing in the Euro 2016 final at the Stade de France on Sunday.
Wales seem to be living some kind of dream at the moment. After topping their group, and then beating Northern Ireland in their first knock-out match, they could have called their campaign a success. However, they came from behind to sweep aside one of the most talented sides in the tournament in Belgium in the quarter-finals with a memorable 3-1 win in Lille - a game that is sure to be talked about for many years to come.
Their progression to the last four did come at a cost, with both Aaron Ramsey and Ben Davies picking up yellow cards that rule them out of tonight's game through suspension.
Portugal have managed to make it all the way to the semi-finals without winning a game inside 90 minutes which is simply remarkable, and they are the bookies favourites to play in Sunday's final.
Three draws from the group stage saw them squeak through into the knock-out stages before they knocked Croatia out of the competition in the dying minutes of extra time in the last-16.
They required penalties to beat Poland in the quarter-finals in Marseille and have their own absentees this evening with William Carvalho suspended, while Pepe is said to be a doubt.
Williams is likely to be one of the players to come in as Wales cope with suspensions. He is likely to take Aaron Ramsey's place in an advanced midfield position with James Collins likely to come into the back three for Ben Davies.
Ramsey's job in the tournament has been to free up space for other players to thrive in, to run the channels, to create opportunities others and be savvy in possession. Everyone will admit Ramsey is a big miss, but Williams has proved a handful whenever called upon so far during this tournament.
He went to Bayern Munich for big money this summer and the teenager has shown flashes of what a top talent he can become, including with his goal against Poland in the quarter-final.
He could be handed a starting role at the heart of the midfield again, but midfielders have been looked after pretty well by Wales during this tournament. It will be interesting to see if he could have that kind of influence again this evening.
He has been one of the standout defenders of the entire tournament, an absolute rock at the back for Wales. While many will be potentially watching James Collins in the Wales defence - as he could replace Ben Davies - Chester's performances have had a big role in bringing Wales this far.
He probably faces his biggest challenge yet up against Cristiano Ronaldo, but it will be one he is confident of passing.