The Swedish Ryder Cup hopeful burst into the 36-hole lead with a spectacular two-eagle, eight-birdie 61, also matching the lowest round of the Tour season set by Adam Scott in Qatar in January.

His previous 61 on the circuit was "only" eight under in the 2006 Wales Open at Celtic Manor, but this was 11 under par and it took him to 15 under at halfway - the joint third lowest in Tour history.

The Players Championship in Florida is golf's richest event and after finishing sixth there last year and eighth in The Masters this April Karlsson fully expected to be back.

But he was given incorrect information about the cut-off point for the world's top 50 to qualify, decided to go to Milan instead and focused on making it the right choice.

Victory on Sunday would take the 38-year-old sixth in the Ryder Cup standings and so far so good.

Karlsson opened with three birdies, then sank eagle putts of 30 and 15 feet on the 554-yard 15th and 526-yard first, then had four more birdies in the space of five holes.

That gave him a chance of the Tour's first-ever 59. He needed a birdie-eagle finish for that and it was possible with the ninth being a 513-yard par five.

But Karlsson parred the eighth before closing with a seven-foot birdie putt to knock one shot off the Castello di Tolcinasco record and move him three clear of South African Hennie Otto.

Karlsson said: "It's hard to rate them, but that's got to be in the top three rounds I've ever played.

"A 59 crossed my mind with two to go, but I've had my problems at the eighth in the past, so I was happy to par it.

"It's good to be here. I wouldn't have been if I'd known earlier I was in the Players, but who knows? It might work out for the best."

Paraguay's Marco Ruiz, joint first-round leader with England's Ross McGowan after a 64, added a 70 to be joint third, while McGowan's 71 left him in a tie for sixth.

Nick Dougherty was playing with Karlsson and was going almost as well until he lost a ball on the 492-yard par-four sixth and double-bogeyed the hole.

The 25-year-old attended his mother's funeral on Tuesday - she died of a heart attack on April 27 - but decided to play because she wanted him to do all he could to make the Ryder Cup team.

In danger of missing the halfway cut after an opening 71 that left him 76th he improved five strokes on that to be seven under and joint 11th.

Otto trimmed Karlsson's advantage back to two when he also birdied the long ninth for a 66 and 13 under aggregate, while Argentina's Estanislao Goya was in third place on 11 under following a 67.

American John Daly bogeyed the second and third, but a birdie on the next got him back to four under, the expected cut mark.

Worksop's Mark Foster, one off the lead overnight, might never have thought he would tee off again eight adrift, but he reduced that to four when he turned in 34 and then eagled the long first to be joint third.

Daly stood four under after eight holes, but that was down in joint 58th place.