Complex sentence: It is the first of the recognised trial races for the Epsom Derby to take place in the season, and although the 1939 winner Blue Peter went on to capture the Derby, it has produced a limited number of contenders for the big race.
Split into simpler sentences: It is the first of the recognised trial races for the Epsom Derby to take place in the season. The 1939 winner Blue Peter went on to capture the Derby, but it has otherwise produced a limited number of contenders for the big race.