SPRINGFIELD, New Jersey (Reuters) - Early second-round play in the PGA Championship resumed after a delay of 41 minutes at Baltusrol on Friday with weather threatening to cause further interruptions in the year's final major championship.

Heavy rain forced a brief suspension after the golfers had been on the course for a little more than an hour, but the rain let up on the humid, overcast day where possible thunderstorms remained in the forecast.

Former PGA champion Martin Kaymer of Germany, who began the day one stroke behind American leader Jimmy Walker, took a step back on the leaderboard in the early going.

Bogeys at the first and third holes dropped Kaymer to two under before a birdie at the par-three fourth brought him back within two shots of the lead.

Australian John Senden covered the front nine in one-under 33 to join Kaymer, British Open champion Henrik Stenson of Sweden, England's Andy Sullivan and Americans Harris English and James Hahn on three under par for the tournament.

One shot behind Walker, who posted a five-under 65 in the first round, were Englishman Ross Fisher and Argentina's Emiliano Grillo. The trio were all among Friday's late starters.

(Reporting by Larry Fine; Editing by Ed Osmond)