Manchester United's Wayne Rooney celebrates his goal against Schalke 04 during their Champions League semi-final first leg soccer match in Gelsenkirchen April 26, 2011. [Photo/Agencies]

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.

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But ensuring they each have a chance to win a fourth European title will require the semifinalists to successfully negotiate second leg matches that are shaping up to be contrasting occasions.

On Tuesday, Barcelona will be hosting a Real Madrid side - and particularly coach Jose Mourinho - still seething following an ill-tempered loss at home last week.

A raging Mourinho suggested there is a conspiracy to help Barcelona go through - one of the inflammatory moments last Wednesday that led to Madrid being hit with six UEFA charges.

Barcelona, though, is also under investigation after an angry scuffle between players and officials from both teams at halftime resulted in substitute goalkeeper Jose Pinto being sent off.

It means the repercussions from the first leg that scarred the reputations of both sides could still be felt long after the final whistle goes at the Camp Nou.

"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 a 2-0 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."

Barcelona, whose lead was secured by Lionel Messi's double, is focused on the health of its injury-ravaged defense.

Center back Gabriel Milito tore a muscle in his left leg in Saturday's 2-1 defeat to Real Sociedad to join an injury list that already includes Adriano and Eric Abidal, although left back Maxwell could return on Tuesday.

That loss to Real Sociedad was Barcelona's first in the league in seven months. But with four games to go, Pep Guardiola's side still enjoys an eight-point lead over Madrid, which also lost to Zaragoza having rested several players.

But 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 loss 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."

Losing, though, in the Champions League is something that rarely happens after first winning away.

Only twice have teams overturned first-leg losses at home: Inter Milan earlier this season against Bayern Munich and Ajax against Panathinaikos in 1996.