Jordan Spieth survived a roller-coaster final round at the British Open to claim his third major title after beating fellow American Matt Kuchar by three strokes in a thrilling duel at Royal Birkdale on Sunday.Spieth carded a one-under-par final round of 69 to finish on 12-under for the tournament but, after three days of consistent golf by the American, it was a remarkable day of highs and lows for the 23-year-old.The Texan, who won the U.S Masters and U.S. Open in 2015, joined Jack Nicklaus as one of only two players to win three legs of the career grand slam before turning 24. Tiger Woods was 24 when he won his third different major.Spieth began the day with a three-stroke lead but saw that evaporate on the front nine, where he made four bogeys and a birdie to enter the turn sharing the lead with Kuchar on eight-under, before he steadied himself and surged to victory.Clutching the Claret Jug awarded to the winner, Spieth, the youngest American to win the British Open and the youngest from any country since a 22-year-old Seve Ballesteros in 1979, said his victory was “a dream come true”.”I drank some wine from the Claret Jug when Zach Johnson won it two years ago and people said that was bad luck. I started to believe them too after nine holes today,” he added.”I’m going to take this back to America which may upset a few of you all but I’ll return it. Thank you very much, what an incredible honour.”Real DramaadvertisementAfter his struggles on the front nine, the real drama began when Spieth drove wildly into the dunes, striking a spectator, on the 13th hole.He was forced to take a penalty stroke after deeming the ball unplayable and, after a lengthy series of deliberations, he played his second shot from the edge of the practice range next to the television trucks.Spieth scrambled to make a creditable bogey out of the par-four hole but that still handed the lead to 39-year-old Kuchar, who was playing the more solid golf as the wind rose and temperature fell.However, the sight of his rival alone at the top of the leaderboard appeared to click a switch in Spieth who responded with a birdie on the par-three 14th, where he was close to a hole-in-one.”When that (birdie) putt went in was my first vocal appreciation of the day. And I knew that we had momentum on our side and we were tied.”All of a sudden I felt and believed that I could win that golf tournament, when 30 minutes prior and really the entire day after the fourth hole I didn’t feel that way,” he said.He then brilliantly sank a 45-yard putt to eagle the par-five 15th and followed that with birdies on the 16th and 17th to banish any thought of a repeat of his U.S. Masters meltdown last year.As he received the trophy Spieth paid tribute to compatriot Kuchar, saying he had enjoyed the battle and describing him as a great champion and class act.”I believe Matt Kuchar will win a major championship. And I believe that he’ll do it sometime soon. He’s a great champion and he’s such a great person,” Spieth said of his rival, who had been given underdog backing from the Birkdale crowd.China’s Li Haotong finished third on six-under-par after a superb last-round 63 left him on the range hoping, in vain, that a few more bogeys from the leading pair might give him a shot at a playoff.Northern Irishman Rory McIlroy produced his best round of the week with a 67 to leave him on five under for the tournament and tied in fourth place with Spain’s Rafael Cabrera-Bello who shot 68.