The LIV Golf Series has lured away some of the sport's biggest names with huge purses while those who joined the rebel circuit are no longer eligible to play in PGA Tour events.
Attempts by Europe's DP World Tour to follow suit have so far been unsuccessful with LIV players still eligible to compete pending a court hearing next year.
Otaegui, who has played in three LIV events, made the most of his opportunity, claiming his fourth European title with a six-shot victory at Real Club Valderrama.
Starting the final day with a six-shot advantage, he fired four birdies and a bogey to sign off with a 68, finishing on a tournament record 19-under-par.
Fellow LIV player Lee Westwood (49) called out the DP World Tour on social media for its coverage of Otaegui, who said he was "very proud" of his win.
"I feel so happy to have my first win in Spain, in front of these crowds, on my favourite golf course in Spain," Otaegui said.
"It's just unbelievable. I'm very happy with everything, the week went perfect. "I'm very happy with the way I managed (on Sunday) because it was my first time with such a big shot difference.
"The plan was just to start strong, forget the shot difference I had and try to beat the others. I played very well until the end. I tried to follow the plan and think I did well."
