The midfielder admitted there was more relief than usual to see the ball fly into the net after a checkered recent record from 12 yards.
"I went out and missed a penalty a few weeks ago and the next one is always hard to take," he said. "You've got to be big enough and stand up and take them and they're the moments. I was very relieved when it hit the back of the net."
City's night became all the harder when Gael Clichy was dismissed for a second yellow card after the break, and Lampard felt that moment was key.
"They were down to 10 men so fair play to them, but I had a feeling that it was going to be our night and it turned out that way," he said.
"We needed to win to stay in the race. Ten points is a huge gap and luckily we've closed that."