Ricardo Quaresma put the Portuguese side in front on the night and overall but Arjen Robben brought the tie level as his shot was fumbled into the net by Porto goalkeeper Helton.

Michael Ballack then netted the winner with his first goal since November from an Andriy Shevchenko nod-down.

Lampard said: "We knew it wouldn't be an easy game, we didn't play well in the first half and put ourselves under pressure, but in the second half we put it right.

"It was a great goal from Michael, he arrived in the box as he does and it was a great finish when we needed it."

Ballack added on ITV1: "I'm happy, we kept our concentration and the second half was better than the first half. I'm happy with the goal but the most important thing is we are through."

Blues manager Jose Mourinho believed equalising so early in the second half was the key to his side's success.

"In that moment [at half-time] we are out of the competition," he said.

"Three minutes later, we are 2-2 on aggregate and it gave us more confidence to get through the game."