BOSTON — The Boston Marathon is getting longer.

Not the race — it remains at 26.2 miles for its 113th edition Monday — but the event that traditionally takes over the Boston streets on Patriots Day has spilled into the weekend with a fun run and competitive miles designed to keep the captive running community busy.

"Other cities have marathons; we have marathon weekend," Boston Mayor Tom Menino said Sunday after holding the winner's tape at the Back Bay finish line of the first Boston Athletic Association Invitational Mile. "When you hear it's marathon weekend, you know it's spring here in Boston — even though the calendar may say something else."

Defending champion Robert Cheruiyot of Kenya will go for his fifth Boston Marathon title, and Dire Tune of Ethiopia will try to repeat as the women's winner in the world's longest-running annual marathon. Ryan Hall and Kara Goucher are the top U.S. man and woman in their respective fields — contenders for titles that haven't gone to an American in decades.

Joining them at the Hopkinton starting line will be more than 25,000 other runners, many of them out-of-towners who make the marathon the centerpiece of a weekend in Boston.

This year their families had a chance to be more than spectators.

In a sold-out 5K on Sunday morning, 4,000 runners from 36 countries got onto the course for the experience of sprinting down Boylston Street to the finish. Among them: 1983 men's winner Greg Meyer — the last American to win the men's race here — and Joan Benoit Samuelson, an Olympic gold medalist and two-time Boston winner.

"I just think it makes it more festive," said Benoit Samuelson, who finished fourth in the women's 5K. "It makes it more accessible for the have family and friends in town who never had a chance to run the course because they couldn't finish a full marathon."

Samuelson, 51, who won the inaugural women's Olympic marathon in Los Angeles in 1984 and in Boston in 1979 and '83, retired from competitive marathon running last year when the U.S. Olympic trials were held here on the Sunday before the traditional race. The event proved to be a big success — not just for the runners, who raved about the course, but for the runners-turned fans who took advantage of the break in training to watch.

That gave organizers an idea.

"The resources are already in place," B.A.A. executive director Guy Morse said Sunday. "A lot of out-of-towners are here with the marathoners trying to get some of the flavor of the marathon. It's an opportunity to get much better use of the inventory and resources."

About half of the entrants in the 5K were family members of Monday's hardcore runners, Morse said, and the other half were runners who can't complete the 26.2-mile distance but wanted to be a part of the festivities. Hundreds watched from the grandstands, many of them raising their hands when the public address announcer acknowledged those registered for Monday's race.

After the races on Sunday, thousands milled around traffickless Boylston Street and posed for pictures under the marathon banner. Sunday's events also included four, one-mile races: high school boys and girls, and men's and women's invitationals stocked with Olympians and national champions.

Darren Brown, who with his father Barry Brown became the first father and son to each run faster than 4-minute miles, won the men's mile in 4:11.6. Anna Willard, an Olympian in the 3,000-meter steeplechase, won the women's Boston Athletic Association Invitational Mile in 4 minutes, 38.6 seconds, less than 2 seconds ahead of Olympic medalist Shalane Flanagan.

"This weekend for me is such a tradition," said Flanagan, who won bronze in Beijing in the 10,000 meters, a native of nearby Marblehead who would come to Boston as a child to see the race. "I thought Patriots Day was a national holiday. I thought everyone stopped to watch the Boston Marathon."

Hundreds of thousands of fans are expected to line the route on Monday as it winds its way through seven suburbs on its way to Copley Square.

Brown, still panting from his victory in the mile, promised to be among them.

"It's fun just to have stuff like this on marathon weekend. For us, it's great to come out here and perform in front of a lot of people who love running — and to go out and support them tomorrow," he said. "I'm sticking around."