The mark bests the old record at Doha of 64, which was set by Andrew Sherborne and David Carter in the 1998 edition of this event.
Karlsson and Pilkington lead by two shots over Frenchman Olivier Edmond and by three over a group of five who shot 6-under 66, including Roger Wessels and Angel Cabrera.
They managed to do so in the calm, early morning conditions of Qatar, when hardly a breath of the annual Shamal (sandstorm) winds were blowing. Pilkington's round consisted of an eagle three at his opening hole - the par-5 10th. He would go on to record seven other birdies. Karlsson's day, which also began on the back nine, was on pace to be even better, as entering the par-5 9th - his 18th of the day - he had already recorded 10 birdies against no bogies.
But a pulled tee shot at the last, which was deemed unplayable and resulted in a penalty stroke, resulted in a bogey six to drop his score to 9-under 63.
Following the round, Karlsson claimed that it wasn't his only bad swing of the day with the big stick, but the rest of his game was good enough to amend: 'Funnily enough, I struggled a bit with my driver all day but otherwise it was good out there. I hit really, really good iron shots and when I hit it in to 10 or 12 feet, I tended to make my chances.'
Likewise, Pilkington tended to make most of his chances. And it started right off the bat with the 20-footer for eagle at his first.
'The putt was a nice way to settle myself down, but really all three shots on the opening hole were pretty good,' the 22-year-old Welshman stated. 'Of course, we had the best part of the day. There was precious little wind and it was a lot cooler at that time of the morning.'
The conditions would, in fact, become progressively more difficult as the day went on. Yet, they never became overly-bearing, and several other players who managed a good day of it were ANZ Players Championship winner Peter Lonard, veteran Eammon Darcy and last week's big victor in the Dubai Desert Classic, Thomas Bjorn.
They all came in with rounds of 3-under-par 69, and reside amongst a large group of 13 others on the mark.
The day was not quite so easy for Welshman Phillip Price, however. The 34-year-old, who played so solidly all year during the 2000 season (including a second-place showing at the WGC NEC Invitational), made two bogies, two doubles and a triple for a score of 78.
Click here for Full-Field scores from the Qatar Masters!