Lampard made a change, bringing on Bradley Johnson for Joe Ledley, and Derby opened Leeds up in the 47th minute but Mount dragged his shot wide with Waghorn just failing to connect.
Former England worldwide Lampard won his first game as manager 2-1 against _ thanks to a last-minute victor, but couldn't repeat the trick in his first home game in charge.
Klich's second goal in two games gave United a fifth-minute lead and while Derby equalised seven minutes later through a stunning free-kick from Tom Lawrence, United went back in front in the 21st minute with a precise header from Roofe.
The first chance of the match fell his way as Harry Wilson drove into the penalty area and picked out Waghorn, who could only scuff his shot into the path of Mason Mount.
It was a superb strike but Derby were level in the 12th minute when Lawrence sent a free-kick from just outside the box over the wall and through the hands of Bailey Peacock-Farrell who should have done better.
Multiple Fatalities in Shooting in Fredericton, New Brunswick
Tim Morehouse, a resident of the complex, said he heard someone shout: "Shut up! We've lost a brother", Secord said. After calling 911, Morehouse said he looked out the window again and saw two police officers lying on the ground.
Kemar Roofe restored Leeds' advantage midway through the half and the striker netted again after the interval before Ezgjan Alioski sealed the rout.
Leeds need not have anxious about the near miss as they made it 3-1 on the hour, Roofe producing a great turn in the area to get clear before rifling a left foot shot into the top corner of the net.
The 24-year-old scored six goals in 42 games last term and with two in two already in this campaign, he will be one to watch throughout Lampard's debut season in management. Carson was called into action to deny Roofe at point blank range with Tomori making a last-ditch block to deny Ayling on the rebound.
Roofe slammed the ball high past Carson to register his second of the game. A deft touch and neat turn created the space he needed to fire a left-foot shot past the helpless keeper. Pablo Hernandez did brilliantly to reach the ball and pull it back before it went over the by-line and Alioski arrived to power a header into an unguarded net.