ABU DHABI: World number one Jordan Spieth was left bemused after becoming the first high-profile player to receive a "monitoring penalty" for slow play in the opening round of the Abu Dhabi Golf championship on Thursday.

The 22-year-old American, playing with four-time major winner Rory McIlroy and compatriot Rickie Fowler, was warned after taking too long to putt on his eighth green  despite the following trio lagging far behind his group.

“It didn’t make any sense to me,” Spieth told reporters after his four-under round of 68.

“The guys behind us hadn't even reached the fairway on a par five.”

Under rules announced this week, players in a group that have been told they are being monitored for time must then play a shot within 40-50 seconds.

Spieth was informed on his ninth tee he had received a warning. A second will result in a small fine in an initiative aimed at trimming 15 minutes from a group’s playing time.

“I just made sure it didn’t affect my round,” said Spieth.

Two late birdies helped the US Masters champion finish two strokes adrift of world number three McIlroy (66) and four from clubhouse leader and US amateur Bryson Dechambeau (64).

“That’s the Rory I have seen win majors. It was spectacular. He didn’t miss many shots,” said Spieth.

“If he keeps striking like that, I’m going to have to make it up somewhere else. I’m not capable of hitting it as far as he does. I hit it short and crooked.”

McIlroy sunk four birdies in the first six holes and will probably be disappointed not to put more daylight between him and the player who has usurped him as the world’s best.

Spieth began slowly, making par on his first five holes before birdies at six and nine.

“I didn't drive the ball well, which is really the key out here, so to shoot four-under with the way I felt with my driver is spectacular,” added Spieth.

“I scrambled pretty well for the majority of the round and then a couple wedge shots just really (stopped) me from making it a great round.”