De Gea has endured a difficult first season in England, making high-profile mistakes early on, then losing his place to Anders Lindegaard after a disastrous display against Blackburn on New Year's Eve.
The Spain Under-21 star was also heavily criticised for his performance in the FA Cup defeat at Liverpool a fortnight ago, to the extend there was even a debate about who would be in goal at Stamford Bridge after a solid contribution from rookie Ben Amos in the win over Stoke.
However, after recovering from the ankle injury that kept him out of that encounter, De Gea was recalled.
And the £18million man responded with a quite exceptional effort to keep out Juan Mata's free-kick in the final seconds of stoppage time to secure a thrilling 3-3 draw.
"I don't know if any other goalkeeper in the country would have saved that shot from (Juan) Mata," said Ferguson.
"His speed and agility is outstanding.
"David knows he had a bad day against Liverpool in the cup. But goalkeepers can have those days.
"Last week's performance will help. He saved us a point.
"When you get a free-kick with the last kick of the game and your goalkeeper makes a save like that, you have to say it's a point saved."