Following a 3-0 win over hosts VFL Osnabruck earlier in the afternoon, Lex Immers gave Cardiff the lead against St Pauli.
Maurice Litka equalised for but Lasse Sobiech's own goal before the break sealed victory for Cardiff.
Frederic Gounongbe, Declan John and Anthony Pilkington scored in the win over Osnabruck.
Summer signing Gounongbe headed Cardiff in front from Fabio's cross during the first half of a game played over two periods of 30 minutes.
Second half goals from Wales international John and  Pilkington sealed victory.
Cardiff City beat St Pauli 2-1 to secure back-to-back wins in the Osnabruck Tournament in Germany.