Slattery had five birdies before closing with a bogey at the par-5, 580-yard ninth hole in taking a one-stroke lead over Marcel Siem and Tim Sluiter.
Four golfers are at 2-under and four more finished at 1-under 70 as windy conditions Thursday made play challenging. More than a dozen players ended up shooting in the 80s and Zhigun Lam wound up at 21-over 92.
Slattery opened on the back nine of the Celtic Manor resort in Wales and was 2-under after three holes. He had eight consecutive pars before a birdie at No. 2. His ball on the third hole nearly found the water but he managed par and added birdies at 5 and 8.
Slattery and was lucky to find his ball in bounds on the ninth, where he ended up with bogey.
"It was very difficult," Slattery said. The wind was stronger than anticipated and if you get round without a bogey it's an amazing achievement."
No one managed that Thursday.
Siem, for instance, had three consecutive birdies and ended up with six on the round but also had three bogeys. Sluiter closed with three consecutive birdies but had two bogeys and a double bogey 5 at the 17th hole earlier in his round.