The 2011-12 Champions League campaign is nearing its final stages as the remaining four teams contest the first legs of their semi-final ties.On Tuesday, German powerhouse Bayern Munich host La Liga leaders Real Madrid in what promises to be an eventful clash between two of Europe's most successful club sides ever.In the other semi a day later, holders Barcelona lock horns with Premier League representatives Chelsea at Stamford Bridge as the Catalans target a second consecutive Champions League final.Once again, Goal.com's experts and correspondents will be on hand to provide you with in-depth coverage and analysis, but here's what they think may unfold on Tuesday and Wednesday.CLARK WHITNEY SAYS ...The home-ground advantage is a key factor heading into Tuesday's clash: Bayern have conceded just nine goals in all competitions on their own patch this season, and shut out quality attacks such as that of Manchester City in the process.Real Madrid are typically better defending away from home, but tend to concede against top-class attacks.All eyes will be on the wingers, but the key to success may be found in the centre of midfield, which will determine the run of play.A first-leg advantage would suit the hosts well, and it will not be the end of the world for Real, who can count on out-gunning the Germans at the Santiago Bernabeu.Chelsea 1-2 BarcelonaBEN HAYWARD SAYS ...Chelsea boosted their morale for this match by hitting five past Tottenham at Wembley on Sunday in the FA Cup, but beating Barcelona will be much more difficult.The last time the sides met was also in the Champions League semi-finals, in 2008-09, when the Catalans advanced to the Rome showpiece following Andres Iniesta's last-gasp goal at Stamford Bridge and a series of controversial refereeing decisions.Chelsea would love to avenge that perceived injustice, but while Barca have grown and grown since Guardiola's first season in charge, the Blues are not the force they were several seasons ago.Expect the Londoners to struggle at Camp Nou (as most teams do) but make a game of it in London.