The Englishman won the Alfred Dunhill Links Championship the week before and carded six birdies - including five on the back nine - in a flawless 65 on Sunday to win his first Rolex Series event.
It had looked like the tournament would be decided by a play-off, with clubhouse leaders Ross Fisher and Kiradech Aphibarnrat alongside Hatton on 20 under par as he stood at the18th tee.
But the 26 year old coolly rolled in his birdie putt from around 15 feet at the last to get to 21 under and clinch the trophy.
Hatton began the day in a tie for second, two shots behind Wallace, but found himself four shots off the lead at the turn after making just one birdie on the front nine.
As he reached the back nine, Hatton caught fire, reeling off four straight birdies from the 12th to catapult himself into contention.
After making pars at the 16th and 17th, Hatton knew he would have to do something special at the last to avoid a play-off.
And he obliged, holing his tricky putt in front of huge crowds at the 18th to win his third European Tour title.
Hatton said: "It's amazing to win one but to win back-to-back and defend in two weeks is unbelievable.
"I knew I needed a low score today, and the front nine was pretty slow and I didn't really get any momentum. I was fighting myself, trying to stay patient and J.B, my caddie, was saying 'good things will come'.
"Although I found it hard to believe, I tried to stay patient. In the end, I guess I got my reward."