Runners take your mark – and mark your calendars for noon on Sunday, March 15. That’s when online registration for the 2009 TD Banknorth Beach to Beacon 10K will begin.

Race organizers expanded the field to 6,000 runners this year – an increase of 500 from last year’s field – but still anticipate the race filling up as soon or sooner than last year’s record of 26 hours.

“We are encouraging – make that urging – anyone who wants to participate in the race to go online and register soon after it opens on March 15 because there’s no way to know how long it will take before it fills up,” said David Weatherbie, the race president.

Online registration is the only way for runners to enter the popular international road race, set for Saturday, Aug. 1 along the coast in Cape Elizabeth. Race organizers stopped using paper registrations in 2008.