United looked to have been cruising to the semi final after they went two goals up early in the first half with goals from Hernandez and Rooney.
But the visitors fought back in the second half and the scores were levelled with goals from Hazard and Ramires. Then in the dying stages of the game, Mata collected a high ball, stepped inside Evans and fired at goal.
The ball was heading into the net but De Gea spread himself to divert the ball wide of his right-hand post with his foot and United could breathe again.
“It was a very good save,” said Ferguson to reporters.
“I saw the replay and it was terrific at a very important time, because there was no doubt we would be out if they had scored at that time.”
Source: United Mad