FRANKFURT, Jan 24 (Reuters) - Peruvian strikers Claudio Pizarro and Paolo Guerrero staged a rescue mission to send Bayern Munich through to the German Cup semi-finals with a 3-2 extra-time win over Mainz on Tuesday.Holders Bayern fell behind to a Mohamed Zidan penalty in the 21st minute and took a long time to get going in the first game back after Germany's long mid-season break.Pizarro grabbed an equaliser with a close-range header eight minutes from time and Guerrero glanced in another header in the fourth minute of extra-time to put Bayern ahead.Petr Ruman equalised with a sweet volley for Mainz in the first minute after the restart before Pizarro clinched victory for Bayern five minutes from time with a 25-metre shot that went in off a post.Werder Bremen are away to third division St Pauli, TSV 1860 Munich host Eintracht Frankfurt and Arminia Bielefeld are at home to Kickers Offenbach in the three remaining ties on Wednesday.Bayern, who hold a six-point lead at the top of the Bundesliga, return to league action at Borussia Moenchengladbach on Friday.'We knew it wasn't going to be an easy task,' Bayern coach Felix Magath told reporters. 'After a long pause it's always hard to find your rhythm.'Mainz looked set to start World Cup year in Germany with a major surprise.Bayern keeper Oliver Kahn had already been forced into a fine one-handed save from Michael Thurk when Mainz went ahead.The home defence blocked a free kick on the edge of the box and as the ball came back in Valerien Ismael tripped Nikolce Noveski and Zidan converted the resulting penalty.Ze Roberto hit the bar with a free kick and Pizarro raced on to a Willy Sagnol pass two minutes before the break only to shoot straight at the keeper.Bayern kept up the pressure and equalised when Michael Ballack headed down a cross from Martin Demichelis and Pizarro beat the keeper.The three goals in extra-time were all top class, particularly Pizarro's perfectly-struck winner.'It was a great Cup tie,' said Kahn. 'Both sides played very well. They had nothing to lose and they gave it everything.'