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  The 19-year-old nephew of trainer Willie Mullins led the 33-1 chance to victory in his first ride in the world-famous race.
  His nine-year-old mount, trained by Mouse Morris, triumphed by six lengths.
  "Everything just went to plan. I couldn't give you a word to describe how I feel," said the jockey.
  The youngster had never even walked the Aintree course before Saturday's race, but he showed his skill to make up three lengths on The Last Samuri after the final fence to take the lead at the Elbow and go on to win.
  Rule The World, who has twice broken his pelvis, was the first horse since the 19th century to claim his maiden win over fences at the Grand National.
  David Mullins was pleased to play his part in the victory for owners Gigginstown House Stud, headed by airline boss Michael O'Leary.
  "Credit to Mouse, he told me before that this is probably one of the best horses he's ever had, he's just had small problems," added the teenager. "So to get the call to ride this one was amazing.
  "I was getting worried that everything was going to plan, and then we hit the fourth-last [fence], and I was kind of delighted once we got back into a rhythm after that that something had gone wrong and it was going to happen coming across the line."
  While there was joy for Mullins, there was frustration for Gigginstown's retained jockey Bryan Cooper, who opted to ride the winner's stable-mate First Lieutenant. They fell at the second.
  O'Leary had sympathy for Cooper, who rode Don Cossack to victory in last month's Cheltenham Gold Cup.
  "Bryan had first choice, and to be fair to him, First Lieutenant has been working out of his skin," he said.
  "When Bryan made the decision on Thursday or Friday we were expecting good ground - had it been that way it would have been a very different race.
  "But the rain came and it favoured horses at the bottom end of the handicap.
  "Had Bryan been able to make the decision at three o'clock today he may well have chosen Rule The World.
  "That's the problem for retained riders: sometimes they have to make tough decisions and they get it wrong."
  After his National win, Mullins rode Ivan Grozny (16-1) to victory for his uncle in the last race of the day.
  "You dream of things like this," he said. "I couldn't ask for much more. and to have a win for Willie is great after he gave me some good rides at Cheltenham."
  Earlier in the day, Paul Townend, replacing the injured Ruby Walsh, had a short-priced double on Yorkhill (3-10 fav) in the Mersey Novices Hurdle and Douvan (2-13 fav) in the Maghull Novices Chase, to help him to the leading jockey award.
  And World Hurdle winner Thistlecrack (2-7 fav) completed a Cheltenham-Aintree double for jockey Tom Scudamore and trainer Colin Tizzard with an easy win in the Liverpool Stayers Hurdle.
target: Teenage jockey David Mullins said he has "never had a feeling like it" after winning the Grand National on Rule The World at Aintree.