(Reuters) - Only a rain delay could slow Zach Johnson as he fired a six-under 65 on Thursday to share the clubhouse lead before first-round play at the John Deere Classic was suspended due to darkness.

The two-times major champion was five-under through 12 holes when storms hit, causing a 3-1/2 hour delay. Johnson returned to finish off a bogey-free round that left him tied with fellow Americans Ryan Moore and Patrick Rodgers at six-under.

Andrew Loupe, eight-under through 14 holes, and Tom Gillis, six-under after 16, will be among those who return to the TPC Deere Run in Silvis, Illinois, early on Friday to finish their opening round.

"We're all used to it," Johnson said of the weather delays. "You have to roll with it. I tend to relax and get in the gym to stay loose. I expected it to be worse. I had one mud ball (after the rain). That's not too bad."

Defending champion and world number three Jordan Spieth is skipping the event this year in light of his decision to sit out the Rio Olympics golf tournament that also started on Thursday.

Moore enjoyed an eventful opening round that started on the back nine and featured an eagle at the par-five 17th hole and a 30-foot par-saving putt at the par-four ninth.

"These are some of the purest greens we putt on," said Moore, who is seeking his first PGA Tour win of the season. "If you hit your line you know they're going to go in."

Johnson is right at home at the John Deere tournament which is being played not far from his hometown of Cedar Rapids, Iowa.

His comfort level has shown as he has not finished outside of the top three in this tournament in his last five appearances, winning in 2012.

"I’m comfortable here, that goes without saying," Johnson said. "I know I can score well here, but if I come here expecting that, I’ve got no chance."

(Writing by Jahmal Corner in Los Angeles; Editing by Frank Pingue)