Graeme McDowell described partner Rory McIlroy as a "phenomenon" after his young team-mate fired Ireland to the top of the leaderboard in the World Cup of Golf Thursday.

McIlroy missed out on topping the European money list at the weekend, losing out to England's Lee Westwood, but said he quickly got over the disappointment.

The world number 10, just 20 years old, sank a 20-foot putt for eagle at the par-five 15th at Mission Hills, but missed repeating the feat on the par-four 16th by a whisker, settling for a birdie.

In total the pair struck 12 birdies and an eagle in their 14-under-par score of 58 in the first-round fourballs, to lead second-placed Argentina by three strokes.

"Rory was probably ready for the professional ranks when he was 15 and 16 and was playing professional golf tournaments at that age," said McDowell.

"I think I only ever played one professional event before I turned pro in 2002. You know, this guy is a phenomenon, there's no doubt about it. I certainly wasn't phenomenal when I was 20 years old. I'm still working out how to be one."

McIlroy finished second in the Race to Dubai, the re-christened Order of Merit, to Westwood at the weekend, even though he went into the final event, the Dubai World Championship, in pole position.

But McIlroy said: "I got over it by the time I woke up on Monday morning to be honest. You know, I'm looking back at it now, and I've had a great season.

"I mean, it's been brilliant. It's been a great, almost like a breakthrough year."

When asked how the pair, both of whom hail from Northern Ireland, felt about representing Ireland, McDowell said: "I'm not really sure of the history of why certain sports are two separate teams and golf is an all-Ireland team."

"It's an honour to represent Ireland and an honour to represent your country doing anything," he added.

Twenty-eight nations are battling for the Omega Mission Hills World Cup in southern China in the 5.5-million-dollar strokeplay team event, which involves two rounds of fourball and two of foursomes.