The security upgrades in Portland included the use of bomb-sniffing dogs, increased police presence around the finish line where the crowds were heaviest, and banning backpacks at the start and finish of the marathon.

Smith also said that after the Boston bombings, organizers focused on making sure the lines of communication between race organizers, law enforcement, and city and state officials stayed open.

"This is a really common, systematic problem everywhere," Smith said. "But we saw really great cooperation on Sunday. We had a perfect day."

Organizers for the Twin Cities Marathon, which also took place Sunday, said they instituted few changes in security practices as a result of the Boston attacks.

"We just asked people to leave their backpacks at home," said Virginia Brophy Achman, event director for the Minnesota marathon.

The team planning the race meets annually to evaluate and modify security. Achman said there was a small increase in the number of police officers monitoring the event this year but, for the most part, it was business as usual.

"For us, what we've been doing has been working, and it all went well," Achman said.

Reuters contributed to this article.