ZACH JOHNSON admitted he had come in under the radar after winning a three-man play-off to win the longest ever Open Championship in St Andrews last night.

Two birdies on the first two of the four extra holes edged him in front and after that the 39-year-old former US Masters champion did just enough to hold off the challenge of South African Louis Oosthuizen and Australian Marc Leishman at the end of five days of play.

By no means the most popular of the many American contenders for this title his victory was tinged with controversy after television viewers questioned how he had tapped down marks on his putting line before officials apparently declared themselves satisfied that he had done nothing wrong.

However the devout Christian won many new fans as he went right round the gallery framing the 18th hole to shake and slap hands with many of them individually having thanked all involved in the event in a slightly rambling but generous victory speech.

“There were a lot of people out there,” he said afterwards.

“That was tremendous. There's a lot of people in Louis's corner, obviously, because he's an Open champion and a phenomenal guy, but for them to stick around was really gracious.”

Few tipped him to contend as he began three shots behind alongside more recent major winners Justin Rose and Adam Scott and three behind Oosthuizen and regular major contender Jason Day at least partly because of his low-key demeanour, his emotions hidden under a cap and sun-glasses.

“I guess that radar is going bonkers right now,” he said, after describing himself as a player who rarely appears on it.

“I don't mind being in that position, you know. I don't know if it's ever really beeping on me.

“I'm not the most charismatic, maybe emotional, fun-packed individual on the golf course, I get that, but I'm just so into what I'm trying to do.”

He claimed, too, that the Open is his favourite tournament and expressed a deep awareness of its importance.

“I'm humbled right now because of what's in my lap and the names that are etched on this piece of metal that is very special,” said Johnson.

“It's the who's who in the game. It's the guys that paved the way. It's the individuals that are historic in sports.”

It had been an afternoon of thrust and counter-thrust as some of the world’s finest golfers took advantage of conditions that were difficult for spectating but ideal for scoring on the front nine of the Old Course in particular.

When Jordan Spieth, heading out in the penultimate pairing, birdied the first just behind Padraig Harrington who had birdied the first two, there was a five-way tie on 12-under-par as they moved alongside overnight leaders Paul Dunne, Louis Oosthuizen and Jason Day.

Soon after, with amateur Dunne’s challenge having inevitably faded, the other four were, along with Day’s fellow Australians Adam Scott and Marc Leishman, part of a six-way tie for second on 13-under, but tellingly Johnson had moved ahead after leap-frogging the pack by reaching the turn in 31, five-under for the day, before birdieing the 10th.

The pack was being shuffled hole by hole with no-one making a clean break, yet just how quickly things could happen was demonstrated when, within four holes as he reached the turn, Harrington found himself six shots behind as he slipped backwards while Johnson, Scott, Spieth, Day, Oosthuizen and now leading the European challenge, Sergio Garcia kept driving forwards.

Both Johnson and Leishman got to 16-under during the back nine, but could not stay there and having bogeyed the 13th and 17th holes Johnson had to hole a 30 footer at the 18th to set the target at 15-under.

Leishman matched it before Oosthuizen also found a birdie when he needed it to do likewise, but in the end fell just short of a second St Andrews win, having lifted the title there in 2010.

“I think I did really well getting in the playoff,” said Oosthuizen, who had a 10-foot birdie chance on his second visit to the 18th green to extend it to sudden-death, Leishman having effectively dropped out of contention by bogeying the first extra hole when the other two birdied it.

“It's never nice to lose a play-off. I've had the experience in 2012 at Augusta, but I'll take a lot out of this week.

“I was really motivated to win this championship this week. I love this place. I've said it a thousand times. I can't wait for it to come back here again.”