LONDON -- With both Barcelona and Manchester United protecting 2-0 leads, a rematch of the 2009 Champions League final is looming at Wembley Stadium later this month.
But ensuring they each have a chance to win a fourth European title will require the semifinalists to successfully negotiate second-leg matches.
On Tuesday, Barcelona will be hosting a Real Madrid team still seething following an ill-tempered loss at home last week. Real coach Jose Mourinho suggested there is a conspiracy to help Barcelona go reach the final, one of the inflammatory moments last Wednesday that led to a disciplinary investigation by European soccer's governing body.
Barcelona also is under investigation after scuffle between players and officials from both teams at halftime resulted in the ejection of backup goalkeeper Jose Pinto.
"We try our best not to let all of this tension affect us," Barcelona midfielder Xavi Hernandez said Monday. "It's almost impossible."
Madrid has already started stoking the tensions as it tries to overturn the deficit and enable Mourinho to reach a second successive final, having triumphed with Inter Milan against Bayern Munich last May.
Madrid has posted a video on its website calling on Belgian referee Frank de Bleeckere to avoid "falling for Barcelona's theater."
"We believe we can do it," midfielder Kaka said. "Madrid can never stop fighting."
Xavi is fully aware of the firepower at Madrid's disposal and the need to frustrate its forward line, including Cristiano Ronaldo, who was rested in Madrid's 3-2 league loss to Zaragoza on Saturday.
"The key will be to dominate the ball," Xavi said. "They will go looking for a result because up to now they've lived off the counterattack, they've been ultra-defensive. But we're also ready in case they tighten up on us."
Barcelona has been buoyed by the news that defender Eric Abidal is available for selection for the first time since March 17 surgery to remove a liver tumor.
Midfielder Andres Iniesta is also set to return following a strained calf that caused him to miss the first leg, when Lionel Messi scored both goals.
Only twice have teams overturned first-leg losses at home: Inter Milan earlier this season against Bayern Munich and Ajax against Panathinaikos in 1996.
Manchester United, which lost to Barcelona in the 2009 final, is certainly confident that Schalke's longest run in the competition will end at Old Trafford.
Key players including striker Wayne Rooney are set to be rested for Sunday's Premier League match against Chelsea, which is just three points behind United with three matches to go.
"I will make some changes on Wednesday without question," United manager Alex Ferguson said. "I will bring Paul Scholes back in, Dimitar Berbatov, Michael Owen. We'll need to do that but I will probably keep my experienced players at the back. We have a big week ahead ... two massive games, so we will regroup and freshen it up."
Schalke has lost three successive matches and was routed 4-1 by Bayern Munich on Saturday.
"It's never good to lose, but in principle we have nothing to play for in the Bundesliga," midfielder Alex Baumjohann said. "We can't hide our heads in the sand, we have to repeat the performances we had before. You always believe."