Grace drove the green on the short par-4 16th hole, a shot that rolled to within five feet of the pin. He then added a birdie on the 18th hole after nearly holing his wedge approach for an eagle, a result that Warren was unable to match.
"I got off to a great start today, and then I fell a bit asleep," Grace said. "The form has been there. I stuck to my routines this week and I played great, and I managed to come out on top."
The victory is Grace's sixth on the European Tour, and second this season. He won the Alfred Dunhill Championship in December by seven shots in his native South Africa.
Grace and Warren were among four co-leaders to begin the day in Qatar, and through 15 holes they were tied at the top alongside Bernd Wiesberger. Grace took control with the shot of the tournament on No. 16, and his bogey-free 66 was ultimately good enough. At 17 under, Wiesberger finished alone in third, two shots off the pace after a 68.
Grace began the week at No. 79 in the OWGR, but that number will improve significantly after his victory. The 26-year-old is projected to move inside the top 50 in the world, a standing he would need to maintain this spring in order to make his third consecutive trip to the Masters.