Germany coach Joachim Loew said there was no greater challenge than defending the World Cup title ahead of the reigning champions' opening game against Mexico on Sunday.

No country since Brazil in 1962 has successfully retained the World Cup, with Italy the only other side to win back-to-back trophies, in 1934 and 1938. "It's the most difficult feat and history has demonstrated that, no one in 60 years has done it," Loew said. "Teams develop and change, players finish their careers and you must bring in new players which makes it the most difficult achievement."