The Oklahoma State standout closed with a 3-under 68 Sunday to become the first amateur to win a European Tour event as he claimed the title at the Open de Portugal.
'It feels great, absolutely great,' said an ecstatic Martin-Benavides.
Martin-Benavides ended the event at 7-under-par 277, one stroke clear of Frenchman Raphael Jacquelin, who chipped in for birdie at the last to put pressure on the winner.
Jacquelin matched the low round of the day as he closed with a 4-under 67 at Quinta da Marinha Oitavos Golfe.
Martin Kaymer also closed with a 67 to jump from a share of 22nd place into a tie for third at 3-under-par 281. He was joined there by Graeme Storm (72), Charl Schwartzel (69) and David Griffiths (68).
Third-round leader Alexander Noren struggled to a 5-over 76 Sunday. That dropped him into a share of 11th place at 1-under-par 283.
After three straight pars, Martin-Benavides rolled in a 9-foot birdie putt on the fourth to gain a share of the lead at minus-5. He chipped to three feet at the par-5 seventh and knocked that putt in to move to minus-6 and into the lead.
The Spaniard pushed his lead to two strokes with a 6-foot birdie putt on 10. Martin-Benavides two-putted for par on the next three holes, while his lead grew to three thanks to a bogey by Jacquelin on 14.
Just when things started looking up for Martin-Benavides, he caught two big breaks to help him remain firmly in the lead. At the par-3 14th, his tee shot landed right of the green in some shrubs, but bounced out and into the rough right of the putting surface.
He got up and down for par from there. Martin-Benavides got another break at the next after his tee shot stopped right in front of a bush.
After consulting with a rules official, the 20-year-old received a free drop away from the bush because he was standing on a sprinkler head. Once again, he got up and down for par to remain at minus-7, two clear of Jacquelin, who birdied the 16th.
'That was one important one,' the Spaniard admitted. 'I got a good break there that I could drop.'
Jacquelin, playing three groups ahead of the leader, chipped in for birdie on 18 to move to minus-6 and within one of the lead.
Martin-Benavides saw the leaderboard on 16 and knew what he had to do.
'On 16, I saw the scoreboard, but I just tried to keep on playing,' he said.
He two-putted the final two holes to secure the title and close out a bogey- free round.
'I was just trying to hit a good shot and play the shot I wanted to,' said Martin-Benavides of his approach shot at the 18th. 'Some times when I had a doubt, I remembered to just stay in the present and keep on hitting shots.'
Afterwards, he said he would not turn professional in the next 14 days, which would have made him eligible for the remainder of the European Tour season.
'I really thought about it, not about winning or anything like that, but about turning professional,' Martin-Benavides stated. 'I've got to play with Oklahoma State. They've given me so many things and been so grateful, it doesn't even cross my mind right now to turn pro.'
Jacquelin, whose lone tour win came at the 2005 Madrid Open, carded three birdies and a bogey on the front nine to move to minus-4. He got it to 5 under with a birdie at 11.
The Frenchman missed the 14th green left and was unable to save par from there. Jacquelin birdied the par-5 16th for the fourth straight day, then chipped in for birdie at the last to end one back.
Alastair Forsyth, Michael Jonzon and Andrew Oldcorn all closed with even-par rounds of 71 to share seventh place at 2-under-par 282. They finished alongside Sven Struver, who closed with a 1-under 70.
Noren shared 11th place with Mark Foster, Stephen Gallacher, Peter Lawrie, Tom Whitehouse and Alejandro Canizares at minus-1.