Rory McIlroy was on target for the fast opening he was hoping for as the early starters made the most of ideal conditions on the first day of the US Open.

All four of McIlroy's major titles have come after a first round in the 60s, a fact the 30-year-old was reminded of by former US Open champion Johnny Miller earlier this week.

"I had a chat with Johnny at the champions dinner and he said if you look at the history of major championships, that first round is so important," said McIlroy, who started the 2011 US Open, 2012 US PGA, 2014 Open and 2014 US PGA with rounds of 65, 67, 66 and 66 respectively.

"I said I know. My first rounds at Augusta and Bethpage this year put me a little bit behind the eight ball and it's hard to catch up, especially as major championships are played on the toughest courses and if you start to chase on those really tough courses, it's hard to do that."

McIlroy's day at Pebble Beach did not get off to the ideal start as he bogeyed the difficult 10th hole, but the Northern Irishman birdied the 13th and then hit a superb tee shot on the par-three 17th to set up another.

After scrambling for a par on the 18th, McIlroy holed from 12 feet for his third birdie of the day on the second to improve to two under par, three shots behind early pacesetter Scott Piercy.

Piercy had covered his first six holes in five under par thanks to an eagle and three birdies and recovered from a double bogey on the eighth with birdies on the 12th and 14th.

Spain's Jon Rahm, who was playing alongside McIlroy, was part of the group on three under alongside Ryder Cup team-mate Tommy Fleetwood, who has finished fourth and second to Brooks Koepka in the last two US Opens.

Fleetwood had also started on the back nine and followed five straight pars with birdies on the 15th, 17th and 18th.