Zach Johnson
Johnson celebrates his second major after a tense playoff at St Andrews. Getty

Zach Johnson has won the 2015 Open Championship after beating Marc Leishman, Zach and Louis Oosthuizen in a playoff on an enthralling final day at St Andrews.

Leishman and Johnson finished the final round 15 under 66 before the last man left on the green in South African Oosthuizen joined them with an exquisite birdie on the 18th.

With a four hole play-off over the first, second, 17th and 18th holes left to decide who would be champion, Oosthuzien and Johnson slugged it out after Leishman fell two shots behind after the first hole.

2007 Masters champion Johnson took the telling advantage with a sublime birdie putt on the second to take a one stroke lead at two under, but created a problem for himself on the 17th, over hitting a left arc. Leishman was unable to take advantage however, finishing the par four hole with another bogey. Oosthuizen followed suit with a bogey of his own, handing Johnson a reprieve that kept him one shot ahead after saving himself somewhat will a neat flick from the rough.

By the final hole. Leishman was now just a spectator with it left between two former Masters champions to battle it out. Both men finished the final 18th for par, a score good enough for Johnson to win the play-off one under.

Jordan Spieth came within inches of joining them in the play-off but came up just short as he finished for par on the 18th to card a 14 under 69 for the day following a costly double bogey on the eighth. The 21-year-old had been looking to become the first man to win the first three majors of the year since Ben Hogan in 1953, having already celebrated Masters and US Open success this year.

Justin Day was also within a shot of joining the trio in the play-off but undercooked his final putt on the 18th to also finish for par.

American Johnson produced a brilliant birdie putt on his last hole to move 15 under but Leishman showed nerves of steel with his next shot on the 15th, retaining his one shot lead with a 10 footer just as Johnson was making his way for the clubhouse. The 31-year-Australian however struck a bogey on the 16th before finishing for par on his final holes.

He and Johnson had a nervous wait watching Spieth. The young Texan had earlier sat one shot off the lead heading to the eighth but an errant tree ensured his tee shot flew 100 feet right off the flag. The Texan finished the hole with a double bogey, leaving him three shots behind the leader only to recover with superb birdies on the ninth and tenth.

On the 16th the young Texan moved level with another tremendous birdie on the 16th from 30 feet in one of the moments of the afternoon, but couldn't keep pace with the leaders.

Adam Scott remained within touching distance of the Claret Jug throughout the day but his challenge officially came to an end with a bogey on the 17th having dropped three shots in his last four holes.

Dustin Johnson, who topped the leader board after the first two rounds, endured a disastrous final day, matching his three over 75 from Sunday's third round, finishing tied for 49th.

Irish amateur Paul Dunne finished the competition six under after stealing the headlines over the weekend while Englishman Danny Willett also settled for sharing sixth place after carding an 11 under 70.

When asked what the words Open Champion sounded like, an emotional Johnson told BBC Sport: "It sounds beautiful. It still sounds extremely sureal. The tone to it is very humbling. I feel blessed to be the champion and honoured to be part of the history of this game.

"To don my name on that trophy is humbling and surreal.

"It has been a week of patience, courage and trust. I can't play any better than I did. I just stayed in it, waited for the opportunities and made a few putts."