The Blues trailed the Championship outfit after 45 minutes, but struck five in the second-half to complete a convincing win.
Lampard revealed after the game that some slight adjustments, and a serious talking to, got the team back on track:
“We upped it,” he told Sky Sports.
“In the first half we weren’t at our best, a bit slow with the tempo of the game and we gave a away silly goal that allowed them to score.
“Once we upped it with a bit of pace in our game you could see a big difference. We had a word with ourselves at half-time.”
The Londoners have endured a tough week of travelling following their FIFA World Club Cup participation in Japan.
But, Lampard refused to use this as justification for Chelsea’s lacklustre start to the game:
“We didn’t make the greatest preparation but there’s no excuse, we had to up it.
“The early goal (in the second-half) gave us the impetus, we believed from then on and we didn’t think we could lose the game.
“Some of the football we played, we opened them up and showed what we could do.”
Luciano Becchio gave Leeds a 1-0 advantage, but Juan Mata, Branislav Ivanovic, Victor Moses, Eden Hazard and Fernando Torres’ strikes put Chelsea into the semi-finals.