Pádraig Harrington believes that Rory McIlroy is the only man who can stop Dustin Johnson winning the Masters if the US Open champion turns up showing the imperious form that has brought him wins in his last three starts.

Out until late May as he recovers from neck surgery but set to commentate for Sky Sports at Augusta National, the Dubliner believes that while McIlroy is the only player capable of stopping Johnson at his best, he sees the American as an unblinking machine who will pay no attention to what the opposition is doing.

While he didn't name McIlroy, Jordan Spieth or any of the other big stars by name,  Harrington made it clear that many are looking over their shoulders for potential threats.

Johnson, on the other hand, appears to be oblivious to what others are doing and  Harrington believes the American has put McIlroy under pressure to step up to the plate and come to the Masters with his A game.

Speaking on 2FM's "Game On" sports talk radio show in Ireland on Wednesday, Harrington said: "DJ is streets ahead of anybody. Well, he's not streets ahead of Rory, but they are certainly setting themselves apart."

McIlroy wants to complete the career Grand Slam on his ninth Masters start but when asked for the Holywood star's chances, Harrington said: "Rory's second favourite. 

"At the end of the day, DJ is playing the golf of his life at the moment. He really has peaked. He is really on form. The thing DJ has that is interesting, because while there are a number of great players in the game at the moment, I get the impression they are all looking over their shoulder for other players; worried about other players. 

"When Tiger was No 1 in the world, he was never thinking about anybody else. He knew his B game was better than everybody else's [A game]. 

"Rory is under pressure with the way DJ is playing to bring his A game and that's tough enough. 

"I think all of the guys are under pressure to bring their A game, trying to beat each other, and that's because there is such a high standard at the top."

Pundits like Paul McGinley believe that McIlroy is at his very best when somebody challenges his supremacy and he took pleasure in denting what has been eight months of DJ-domination by snatching the FedEx Cup from under the American's nose in Atlanta last year.

Harrington sees lots of potential winners that push wonderkids like the fiery Jon Rahm onto a secondary plane for the Masters.
 
"There are half a dozen guys who are as good as each other, especially when they turn up and play," Harrington said. "But saying that, DJ doesn't think very much. I don't think that DJ looks over his shoulder. I don't think DJ worries at all and is the guy most likely to turn up and play his own game next week. 

"If he does turn up and plays his game and performs, he is going to be the winner. Rory is the only guy capable of beating him at this very moment." 

Basque star Rahm made a run at Johnson in the WGC-Mexico Championship before fading to tied fourth with a couple of untimely three putts.

The 22-year old then produced another incredible performance to reach the WGC Dell Technologies Match Play final, coming back from five down after eight holes in the decider to take Johnson all the way to the 18th.

Harrington sees Rahm as a future world No 1 and European strong man. 

But he also believes the temperamental Spaniard is not quite the finished article and that he may struggle to become the just the second debutant to win the Masters after Fuzzy Zoeller became the first to win on his debut in 1979 — or the third if you count the inaugural Masters Tournament won by Horton Smith in 1934.

"This lad Jon Rahm, we are looking at a future world No 1," Harrington said. "We are looking at a player who will be ensconced in the top 10 in the world for a good period of time. 

"We are looking at a European No 1. This guy is going to play 10 Ryder Cups. He is going to be our No 1 player in Ryder Cups. This is a big star going forward. 

"Can he win at Augusta straight from the gun? If I hadn't seen him at the Match Play I might say yes. But as we all saw in the last round of the Match Play, he lost the run of himself against DJ. He was getting angry, and he lost his composure. 

"He is going to be tested at the Masters in a major. It looks to me that as good as he is — and he really is good — there's just a little bit of learning in him. I am not saying he can't win the Masters, but my attitude would be that he needs more time to be the polished article.

"As well as that there are maybe half a dozen players in the game of golf at the moment that are really special. You've got Adam Scott, Phil Mickelson and Bubba Watson, who are Augusta specialists. You have to give them a chance around Augusta more so than at any major." 

Add Spieth, McIlroy and the form player Johnson and the first major of the year could not ask for any more explosive potential.