Fans chanted and caroused outside the ballpark and nearby bars after Boston vanquished the St. Louis Cardinals 6-1 in Game 6. Several fans were seen giving high fives to police officers.
"Words cannot describe how I feel," said Sam D'Arrigo. "This is what being a Boston fan is all about."
An excited Boston Mayor Tom Menino tweeted: "Get the ducks ready, we're having a parade."
The Red Sox have now won three World Series in a decade, but they hadn't won at home since 1918.
Police reported no significant problems immediately following the game but said they were ready for post-game celebrations and any unruly fans.
Throughout the night, the department tweeted cautionary messages, encouraging fans to "Celebrate with pride" and "Celebrate responsibly."
In St. Louis, fans were disappointed that the Cardinals lost. Many watched the game 1,200 miles away from the comfort of their couches. Some tourists favored the 26th-floor view of the Gateway Arch over the play-by-play of a third consecutive loss in a series that earlier looked like it could have ended at Busch Stadium after the Cardinals won two of the first three games.
"It's pretty quiet in here," said Coltier Blakely of Mexico, Mo., who was in town for a statewide meeting of community college administrators.
Earlier in Boston, President Barack Obama delivered a talk on his embattled health care reform. He departed Boston an hour before the game began.
Police and bomb-sniffing dogs swept through Fenway as hundreds of fans gathered outside in the afternoon. Scores of officers stood outside the park, directing traffic, giving directions to fans and standing ready for what was likely to be a long night.
Boston has hosted several celebrations over the last decade as the Celtics, Patriots, Bruins and Red Sox have all won titles since 2004, but some of the post-championship partying has caused problems. In 2004, a 21-year-old college student was killed by a pepper pellet fired by Boston police during crowd-control efforts following the Red Sox win in the American League Championship Series. In 2008, a 22-year-old man died after police took him into custody during street celebrations of the Celtics' title.
Chris LeBlanc of Glocester, R.I., skipped class last spring to watch the Red Sox's season opener. On Wednesday he was at Fenway with his father Michael, hoping to score tickets.
Despite a dismal 2012 season LeBlanc, 18, said he always felt good about the team's chances this year. "I was optimistic," he said.
Michael LeBlanc, 45, shook his head and smiled. He remembers well the decades of disappointment, the talk of curses and the blown chances. He knows what a treat it is to have a shot at three World Series wins in a decade.
"He doesn't know how good he has it," he said.