Ross Barkley scored a second-half victor, as the Blues booked their spot in the last four, where they take on Manchester United at Wembley.
Lampard reveals he could have subbed the greater part of his group at half time, guaranteeing they got “fortunate” in the game.
The Chelsea supervisor took off Mason Mount, Billy Gilmour and Reece James at half time, following a helpless showcase.
“I could have made seven or eight subs at half time. We got lucky. If we turn up like that again we have no chance.
“It was the worst we’ve played since I’ve been here.
“The first half was not what we are used to in terms of our performance. We lacked urgency and intensity. I made three subs but it could have been more and different subs,” he told the media after the game.