Florida: McIlroy's composed round at Sawgrass included an eagle at the 16th, while Tiger Woods shot a one-over-par 73.

"Anything in the 60s is a very good start," said 26-year-old McIlroy.

McIlroy is two shots off the lead shared by Japan's Hideki Matsuyama, Canada's David Hearn and American pair Kevin Na and Charley Hoffman.

In contrast, Spieth struggled and said that only good putting had prevented him from failing to break 80.

The American went 58 holes without a bogey at Sawgrass last year before eventually finishing fourth behind winner Martin Kaymer but the 21-year-old bogeyed his first two holes on Thursday after starting at the 10th.

"Sometimes you have bad breaks and have a bad day. This wasn't one of them. I really struggled out there," he said.

McIlroy's only dropped shot came at his 10th hole having earlier negotiated the infamous island green on the par-three 17th with a safe two-putt par.

McIlroy, fresh from his WGC Match Play triumph in San Francisco last weekend, said his round was a legacy of adopting a largely conservative approach.

"You just have to be very, very patient. I have a lot of pars on my card," added the world number one.

"It can jump up and bite you very quickly and you have to know sometimes that par is a good score and you move on."

Former world number one Woods, who earlier in the week said the recent end of his relationship with US Olympic skiing champion Lindsey Vonn had been "brutal", birdied the 16th and 17th but bogeyed the last.

Courtesy: BBC Sports