The Blues came from behind to win 5-1 at Elland Road in the quarter-finals after Luciano Becchio struck first and Lampard suggests it was a dressing room chat which sparked the reigning Champions League and FA Cup winners.
"We upped it,'' Lampard 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 away a 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.''
He added: "We didn't make the greatest preparation but there's no excuse, we had to up it. The early goal 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.''