Athletic Bilbao are hoping another strong performance at their San Mames home can see them past Sporting Lisbon in Thursday's semi-final second leg and into next month's Europa League final.
The Basque club were too strong for Manchester United and Schalke earlier in this season's competition, but their chances of reaching a second European final -- and first since 1977 -- are on a knife-edge after a 2-1 defeat in the first leg in Lisbon last Thursday.
Athletic had taken the lead courtesy of a Jon Aurtenetxe goal in Portugal only for Emiliano Insua to equalise and Spanish international winger Diego Capel to give Sporting the upper hand.
However, midfielder Ander Herrera remains confident as to Athletic's chances in the return.
"A 1-0 win would put us through, so we need to be optimistic," he said.
"We are strong at San MamÃ©s in front of our fans and we just need to go out and demonstrate that.
"We have a result that we can overturn. We have to improve because there were things to improve, but we also have to be optimistic."
After missing Sunday's 1-0 win at Racing Santander in La Liga due to an eye problem, young star Iker Muniain is set to return for Athletic.
Meanwhile, Sporting make the trip fresh from recording a fourth straight domestic league win, 3-2 at Nacional, and should be able to welcome back Matias Fernandez, an attacking threat who has played under Athletic coach Marcelo Bielsa for the Chilean national team.
Sporting are looking to follow in the footsteps of compatriots Porto and Braga, who met in an all-Portuguese Europa League final 12 months ago.
However, If Athletic make it through they will set up the first all-Spanish continental final since Sevilla beat Espanyol on penalties at Hampden in the UEFA Cup in 2007.
The other semi-final might have been decided last week, but a Ricardo Costa header in stoppage time at the Vicente Calderon gave Valencia a precious second away goal in a 4-2 defeat against Atletico Madrid.
Valencia have blown hot and cold in recent times, but they were on fire on Sunday in a 4-0 thrashing of Betis at the Mestalla that strengthened their grip on third place in La Liga.
In a domestic competition utterly dominated by Barcelona and Real Madrid, they have established themselves as the 'best of the rest' since Unai Emery took over as coach in 2008.
But, with Emery set to depart at the end of this season, this is his last chance to leave a legacy of silverware.
Brazilian attacker Jonas, who netted Valencia's first goal in Madrid, believes the tie is still very much alive and says the home side need not come out with all guns blazing.
"The second goal kept us alive and we will be fighting to reach the final. We can do it. We have the quality," he said.
"We will have to play to our very best. This is our most important game of the season. We have 90 minutes to turn the tie around so we need to remain calm.
"We cannot afford to play a crazy attacking game and leave spaces behind for them to exploit. There needs to be a balance."
Atletico beat Valencia in the quarter-finals on the way to winning the Europa League two years ago and their coach Diego Simeone said a potentially poisonous Mestalla atmosphere could make things even more difficult for the home side on Thursday.
"They will be desperate to produce a much better performance but they have a very demanding support who will not accept things going against them," said the Argentine, who won the UEFA Cup in his playing days with Inter Milan.
"The Valencia players know their fans will not allow them to make any mistakes.
"I don't think the tie is decided," he added as a note of caution.
"I think it is still wide open because they are a great side and I imagine they will be angry too."
Defender Diego Godin returns for Atletico after missing the first leg through suspension, while Valencia must do without French left-back Jeremy Mathieu.