Weimann, against his former club, scored with his second touch after coming on as a substitute, and Szmodics picked up where he left off last term when he was the division’s top scorer.
Japanese forward Ohashi added a fourth before Kane Wilson headed a consolation for the Rams.
The opening goal came after Lewis Travis’ piercing run towards the penalty area led to Makhtar Gueye receiving the ball in space on the right.
Nelson prevented Ryan Hedges from getting a decisive touch to Gueye’s pull-back but the ball ran to Dolan, who smashed home from close range.
The breakthrough came after Senegalese striker Gueye, making his debut following his recent move from Belgian
club RWD Molenbeek, had an early chance but shot wide after collecting Travis’ clever pass.
Derby barely threatened in the first half but almost equalised direct from a corner early in the second, Nathaniel
Mendez-Laing’s delivery was clawed away at the near post by keeper Aynsley Pears.
