Rahm came from two shots back at the start of the day in signing for a five-under par 67 and also playing the final hole in five-under for the four days for his 20-under par tally in Madrid.
"It's been unbelievable. 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".
Rahm then birdied to one clear on 18-under but dropped a shot on nine with Dunne parring four holes in succession from the sixth with the duo heading to the closing nine locked at 17-under.
Trump again calls Comey a 'slimeball' ahead of book release
He maintains an air of rather self-conscious rectitude throughout, while finding much to disapprove of in the world around him. He thought he needed to do it to prevent any cloud over Clinton's widely expected victory on Election Day.
The 23-year-old Spaniard earned his third European Tour win a week after finishing fourth at the Masters in Augusta. George Coetzee was a shot further back in fourth after a 63. You can tell how excited everybody is, I felt that tension, I felt that stress, I felt everything magnified. As a golfer it's hard to deal with the public's emotions, so I tried to isolate myself and that's perhaps why I didn't play my best golf. "So being able to win this as a pro and do this for them and the Spanish people feels great".
Ireland's Paul Dunne, who headed to the last day leading by one, finished second with a round of 71 for an 18-under par total. Everyone seemed to want me to win. I've been blessed to be national champion with the Spanish Golf Federation many times, European champion and world champion representing them.
Elvira handed the title to Rahm when he hit his tee shot into the water at the 17th and made a double bogey just moments after the champion's tee shot hung up on the bank, allowing him to save what turned out to be a crucial par.
Poulter's 75 left him on nine under in a tie for seventh, as Kim was eventually beaten in a play-off by Japan's Satoshi Kodaira, with another Englishman in Matt Fitzpatrick in a tie for 14th on eight under.