The Spaniard was just two behind when he birdied the 12th, but that was matched by Sullivan who then gave himself plenty of breathing space with two lengthy putts for back-to-back birdies at 14 and 15, and his lead was back to six shots when Otaegui dropped his first shot of the final day at the penultimate hole.
Otaegui parred the last to ensure he would finish in outright second on 20 under par, just pipping the talented young Dane Rasmus Hojgaard, who climbed 13 places up the leaderboard to earn a podium finish with a seven-birdie 64.
But the stage was left clear for former European Ryder Cup star Sullivan, who finished in style when he clipped a wedge to 12 feet at the last and rattled it home for his 25th birdie of the week.
“It feels like the weight of the world has been lifted off my shoulders,” he said. “I’m back in the winner’s circle. I’m feeling proud of myself to come back and get that W in the manner I did today.
“It didn’t feel like a seven shot lead out there. When I got on 12 and saw Adrian was two behind and breathing down my neck, so it was just nice that I could keep pressing on at the end there. The putter just got hot.”
Sullivan’s compatriot Steven Brown was unable to keep pace with his playing-partner and closed with an erratic 70 to slip to fifth place and one behind Wilco Nienaber, who was a late addition to the field on the eve of the tournament.
The South African got the start when John Catlin was withdrawn from the event for breaching the European Tour’s Covid-19 regulations, and Nienaber took advantage of his late call-up as a closing 66 lifted him to a fourth-place finish on 18 under – by far his best performance in his 11 Tour appearances.
WHAT’S IN THE BAG OF THE WINNER:
Driver: Ping G410 Plus, (9°, Aldila Rogue 130 Silver 60 TX shaft)
3-wood: , (15°, Aldila Rogue 130 Silver 70 TX shaft)
5-wood: Ping G, (18°, Aldila Rogue 125 Silver 80 TX shaft)
Irons: Ping iBlade, (4-5), (6-PW, Nippon Modus 120-X shafts)
Wedges: Ping Glide Forged, (50°, 54°, 60°, Nippon Modus 120-X shafts)
Putter: Ping Heppler Anser 2