The Blues boss took the opportunity to give 22 different players a run out at Dalymount Park, with Willy Caballero, Cesar Azpilicueta, Danny Drinkwater and Pedro all featuring in a strong Chelsea starting line-up.
It took Michy Batshuayi just eight minutes to score the first goal of the Lampard era, firing home instinctively from six yards after he collected the rebound from Kenedy's deflected shot.
Pedro skied a free-kick over the crossbar as Chelsea dominated the first half, although Caballero was forced into a first save when former Brighton and Hove Albion midfielder Danny Mandroiu forced the Argentine goalkeeper to punch a dipping shot away.
Lampard sent on 11 different players after half-time, with returning loanees Kurt Zouma, Izzy Brown and Tiemoue Bakayoko given the chance to impress.
Teenage midfielder Billy Gilmour and Bakayoko both squandered second-half chances as Chelsea failed to extend their lead, and the hosts passed up a number of opportunities to test Chelsea's second-half goalkeeper Jamie Cumming.
But Bohemians midfielder and trialist Eric Molloy made no mistake when he burst into the box with just over a minute left on the clock, lashing the ball high into the net beyond Cumming to deny Lampard a first win.