Mamedyarov chose 4...Bc5, a more combative move that leads to complicated positions. The move played by Duda is more reliable.
1. c2c4  1... e7e5  2. b1c3  2... g8f6  3. g1f3  3... b8c6  4. e2e4 This system is very popular nowadays. It was used, for instance, by Niemann in his victory against Mamedyarov in the Sinquefield Cup.