The postponement of Monday night's NHL game between the Bruins and Ottawa Senators, and the cancellation of Tuesday's NBA game between the Celtics and Indiana Pacers -- both events to be held in Boston -- were the most tangible reactions by sports officials to the explosions at the marathon finish line that killed at least three people and injured more than 130 others.
The NFL's New England Patriots, meanwhile, canceled a pre-draft media event that was scheduled for Tuesday at Gillette Stadium.
The NBA said Monday that the Celtics-Pacers game will not be rescheduled. The teams already have clinched playoff berths and are locked into certain seedings in the Eastern Conference.
A makeup date for Bruins-Senators was not announced; no other events from top professional leagues around the country were immediately called off.
Still, other effects of the explosions could be seen quickly, such as bomb-sniffing dogs sweeping the arena before the doors opened for an NHL game in Nashville between the Predators and Canucks, and armed police officers posted in front of each dugout at the Padres-Dodgers baseball game in Los Angeles.
More toughened measures are expected as security is calibrated for upcoming major events that draw big crowds including the Kentucky Derby on May 4, and the Indianapolis 500 on May 26.
The Associated Press contributed to this story.