Graeme McDowell says “it could be incredible what Rory McIlroy will achieve in the sport” following his dramatic career Grand Slam-clinching Masters triumph.

McDowell, the 2010 US Open champion, said he was among the millions of TV viewers who “lived every shot with him” during Sunday’s rollercoaster of a final round at Augusta as he also ended an 11-year major drought.

“He’s now a legend of the game. To win the Grand Slam is something a lot of players don’t even come close to touching,” said McDowell as he recalled his first-ever round at St Andrews with a then 18-year-old McIlroy on the eve of the Dunhill Links Championship in 2007.

At the age of 35, McIlroy has achieved the career Grand Slam goal he spoke of as an eight-year-old in a 1998 BBC TV interview.

And the “floodgates could now open” for him, McDowell said.

“I still look at him as a kid that looks like he’s got 10 or 15 years of career ahead of him,” added McDowell, who played alongside McIlroy in the victorious European Ryder Cup teams in 2010, 2012 and 2014.

“As in any sport, or in any facet of life, when you’ve absolutely climbed to the top peak of what you want to achieve in your life, where do you go from there?

“Some people can be just like ‘that’s it’ and maybe not do a lot more in their career. Others people can kick on and the world is their oyster and he could go on to win four, five, six more majors from here.”