Meanwhile, Australian Paul Archbold is four shots off the pace after shooting an error-free three-under-par 69 at St Andrews on Thursday.

Long the dominant figure in over-50s golf, Langer arrived as the man to beat on. And not much has changed.

While Langer's five-under 67 wasn't the best score over the Old Course, the German's lofty presence on the leaderboard will have the attention of every other contender.

Langer is tied for fifth alongside former US PGA champion David Toms and another American, Scott McCarron, with the trio one shot behind former Ryder Cup captain Paul McGinley and Canadian Stephen Ames.

As many as 16 players shot 68 or less, a figure that almost included 68-year-old Tom Watson, on a bright and breezy day.

Triplett plays from the 3rd tee during The Senior Open. PHOTO: Tony Marshall/Getty Images.

The seven men atop the leaderboard were all at least three-under par by the turn. But it was a different matter coming home. No one in the 144-strong field was better than three under for their final nine holes.

Wiratchant's round was highlighted by a run of five straight birdies from the 3rd hole. Four more followed, with dropped shots at holes 13 and 17.

David McKenzie finished two-under par and equal 27th on the congested leaderboard.

The Victorian birdied three holes on the front nine and one at the start of the back nine, then bogeyed two, before recovering with a birdie on the 18th.

Countryman Peter Fowler had a forgettable round, carding four birdies and three bogeys, to end one-under par.