The 41-year-old Australian moved to within two shots of the Belgian leader on Sunday as he started his final nine holes on the challenging Yas Links with a couple of impressive birdies.
But Scott, seeking his first victory since back-to-back wins in the Australian PGA and the Genesis Championship on the PGA Tour in 2020, then missed two shortish birdie attempts, from 11ft and 7ft, at the next two holes which could have brought him alongside Pieters.
With those chances squandered, the 2013 Masters champ then made a mess of the par-five 15th when his short chip failed to make the green and rolled down the slope straight back to him.
That six effectively sank his hopes amid a crowded leaderboard and Scott finished up with a three-putt bogey on 18 that meant he ended in joint 10th on a six-under total after his level-par 72 left him four shots behind Pieters.
The Belgian, who turns 30 next week, produced an assured final round, also a 72, to earn the biggest victory of his career and a 1.16 million Euros ($A1.8 million) winner's cheque.
He finished one shot clear of Spaniard Rafa Cabrera Bello and Indian long-shot Shubhankar Sharma, to take his sixth European tour title, with Frenchman Victor Dubuisson tying for fourth alongside Viktor Hovland.
Scotland's Scott Jamieson, who had led the way for the first three rounds, ended with a disappointing five-over 77 to finish alongside Scott in 10th.
"I'm happy I can finally get my caddy, Adam, a gold bib (for winning a Rolex Series event)," said Pieters, who, like Scott, shot a final-round 72.
"I chickened out on the last. I was gong to go for it but I was told I was two ahead so I decided to lay up and I made a (par) five which was fine.
"I just hope all the juniors back in Belgium are watching this.
"I used to think it was impossible, but when Nico [Colsaerts] came on the scene and started winning that was inspiring and I hope that is the same for the kids back home."
Rory McIlroy also made a charge, moving to within two of the lead, but he had three bogeys in the final five holes and ended up in a tie for 12th.
With PA
