As Rahm closed with a five-under 67 to win his third European Tour title on 20-under par and become only the sixth Spanish victor since 1972, Dunne had to console himself with a late birdie that denied Spain's Nacho Elvira a share of second at the Centro Nacional de Golf.
That sent the 31-year-old down to third behind overnight leader Paul Dunne, who was kept at bay by Rahm with a trio of birdies on a flawless back nine.
"When I made the decision to come straight from Augusta it wouldn't be to just show up and walk around, I wanted to win this tournament", Rahm said.
The victory is Rahm's first as a professional in his homeland after claiming seven national amateur titles at various age levels and adds to his two Rolex Series triumphs in Ireland and Dubai last season.
Police arrest Vasco woman for torturing 8 'adopted' minor girls
She was produced before the Judicial Magistrate First Class (JMFC), Vasco, on Sunday and remanded to five-day police custody. Her father accompanied to the police station where she filed a case against the accused, the officer said.
"Being able to win this as a pro for the Spanish people feels great, it's hard to describe". Rahm came out strong every round at Centro Nacional de Golf and fired all four rounds in the 60s for the victory. There, he escaped with a par after nearly sending his tee shot into the water, the ball just holding up in the rough. George Coetzee was a shot further back in fourth after a 63.
"It's been unbelievable", Rahm noted.
"It's been fantastic. It's truly been the hardest Sunday I've ever had in any tournament that I've won because the crowd wanted it so much and I wanted it so much". You can tell how excited everybody is. I felt that. And it was hard to deal with. The win still won't come but this follows T4 in the Oman Open and second spot in the Maybank Championship so three top fives in four starts represent the most consistent spell of his career since he came on Tour in 2009.
Bidding to become the first wire-to-wire victor since Neil Coles in 1973, the Greystones star (25) had to make a 10-footer for birdie at 18th just to finish two shots behind the conquering home hero. Everyone seemed to want me to win.
Rahm edged back ahead with a close-range gain at the seventh, as Elvira missed the sixth green and dropped a shot, before the world No 4 cancelled out a three-putt at the ninth with a birdie at the par-five next.