Rahm becomes just the sixth Spaniard to win the Open de Espana since the European Tour was formed in 1972, following on from Antonio Garrido, Seve Ballesteros, Sergio Garcia, Alvaro Quiros and Miguel Ángel Jiménez.
After Rahm had stamped his mark on proceedings with birdies at the first, second and seventh holes in the final round, the tournament was decided on the short 17th.
An all-Spanish play-off looked on the cards until Elvira found the water with his tee shot on the penultimate hole and, after seeing a brilliant chip for par lip out, had to two-putt what looked like a routine finish.
The 23-year-old held off closest challenger Paul Dunne with his final-round 67 to earn a third victory in his last 10 worldwide starts.
"When I chose your decision in the future direct from Augusta rsquo & it wouldn;t be to show up and wander around, " I wished to get that particular tournament", Rahm told reporters.
Rahm began the day third on the leaderboard, two shots behind Dunne, who had set the pace in the first three rounds, and one behind Elvira. George Coetzee was a shot further back in fourth after a 63.
The tournament was eventually decided on the short 17th as Rahm escaped with a par after nearly sending his tee shot into the water, the ball just holding up in the rough.
"It's been fantastic", continued Rahm.
That left Dunne or even Elvira needing an albatross on the 18th to induce a tie an order with Dunne having a birdie into pip the Spaniard to location. You can tell how excited everybody is, I felt that tension, I felt that stress, I felt everything magnified. I've been blessed to be national champion with the Spanish Golf Federation many times, European champion and world champion representing them. "They played a huge part, I came for them mainly so I'm just glad I can win this one for the Spanish people".
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