They held on to one another with each pass, bit their nails as they watched what couldn't possibly be happening, cursing as the Giants persistently stayed in the game and inflicted the final insult: a touchdown with less than a minute left.
Tears flowed with Tom Brady's game-ending incomplete pass.
Before it was over, Boston collectively held its breath. Fans packed bars to watch the city's sixth major sports championship game in as many years. This was the only one we lost.
For many, what happened last night was not just another football game or another Super Bowl; it was the culmination of a deep longing for the team to go 19-0, for the New England Patriots to define sports perfection.
In the end, they could not.
At Stadium Sports Bar & Grill in South Boston, packed with about 400 fans - many in Patriots jerseys - Colleen Flynn, 26, of Medford, was distraught.
She and others couldn't understand how it ended as it did.
"It's very sad - a sad end to the perfect season," Flynn said. "I didn't think this could happen."
Added Jayce Cardoso, 30, of Hudson: "Disappointment. Pure disappointment."
For city officials, it was another test of their ability to check the mayhem that marred previous championship games, such as in 2004, when police fired pepper-pellet guns into a post-Red Sox victory crowd, killing Victoria Snelgrove, a 21-year-old Emerson College student. Earlier that year, after the Patriots won their third Super Bowl, fans overturned cars and started fires throughout the city. James Grabowski, 21, died when the driver of a sport utility vehicle plowed through a crowded Symphony Road.
Working with State Police, local universities, and neighboring police departments, among other agencies, city officials put nearly 1,000 officers on the streets, ordered parking restrictions and street closings, and monitored events from a command post at Boston Police Headquarters.
"We're strategically placed in areas around the city," said Elaine Driscoll, a police spokeswoman, as the teams took the field last night.
After the game, police began opening blocked streets. Shortly before midnight, they reported having made no arrests.
"Everyone seems to be heading home," Driscoll said. "The evening thus far has been without incident."
For Pats fans who made the 3,000-mile trip from Boston to Glendale, Ariz. - and watched the perfect season come to a very imperfect end at University of Phoenix Stadium - the Pats loss came like a punch in the throat.
"They blew it," said Aaron Miller, a 19-year-old college student from Needham who attended the game with his father, Stephen.
All week in Arizona, Pats fans had paraded on the streets of Scottsdale and Phoenix talking about history. They routinely taunted the football gods, wearing 19-0 stickers, painting 19-0 on their faces, carrying 19-0 banners, chanting 19-0 from karaoke microphones.
But history didn't play exactly the way they expected. Pats fans who were among the 70,000 in attendance yesterday were quiet much of the game, stunned that the Giants were even competing.
Late in the fourth quarter, chants in one upper-deck men's room - "Here we go, Giants, here we go" - went unanswered by sullen Pats fans. And when the Giants finally stunned the Pats just after 10 p.m. eastern time, Pats fans - who hailed from Salem to San Diego, Rockland to Las Vegas - found themselves at a loss for words in the Arizona desert.
"I'm totally shocked. I'm completely shocked. I have no words," said Kaye Jackson, the mother of Patriots wide receiver Chad Jackson, who had flown to Phoenix from Hoover, Ala., to attend her son's game and sat in the upper deck among other Pats fans.
"To get to 18-0 and lose the last game," said Chad Jackson's sister, Devin, who was also at the game, "it just makes you want to go home, lay on your pillow and cry."
Back in Harvard Square before the game ended, a group of optimistic fans pressed against the window at Cardullo's Gourmet Shoppe to watch the game on a 42-inch plasma TV.
"This is history, you are watching history," said Tony Abruzzi of Cambridge.
Across the street at Pizzeria Uno, Derice Darlington, 22, a student at Wellesley College, said she was defying her mother's side of the family, which comes from New York. "My roots, my heart, are with the Patriots," she said.
Throughout much of the city during the game, the streets looked like a ghost town, with many restaurants without televisions empty.
At the Purple Shamrock in Faneuil Hall, the intensity pumped through Mark Sherbertes's veins.
"I could do 150 push-ups right now," said Sherbertes, 41, of Centerville.
At the Joshua Tree Bar & Grill in Allston, Patriots and Giants fans traded cheers.
"I'm always surrounded by New York fans, and I come to a Boston bar and somehow I'm surrounded by them as well," complained Morgan Wenzel, 23, of Brighton.
Her boyfriend, Mike O'Shea, 23, of Allston, wasn't concerned about rooting for his team, the Giants, in Boston.
"We both cheered for the other's team all season, but now it's tough," he said.
When it was over, dejected Patriots fans streamed out of the bar, covering their Patriots jerseys with their coats as they walked to their cars in disbelief.
In the back of the bar, a small group of Giants fans hugged, jumping in unison.
"I feel ecstatic. The Patriots are the best team ever, and we just beat them," said Ian Manheimer, 24, who grew up in Manhattan.
Their chants were like daggers to all Ross Brodmerkle's hopes.
He couldn't imagine anything worse.
"This is the biggest upset of mankind," said Brodmerkle, 21, a student at Emmanuel College. "The worst team in the world beat the Patriots."
John C. Drake of the Globe staff and Globe correspondents Emma Stickgold, Caitlin Castello, Emily Canal, and Daniel Peleschuk contributed to this report.