MONTREAL — What began as an eardrum-rattling eruption of hockey joy ended in an eye-burning cloud of tear gas as looters and police squared off on streets that had just celebrated a memorable Montreal Canadiens win.

And a city with a history of hockey greatness, as well as hockey-related violence, wrote two chapters on the same night.

A playoff win over the mighty Pittsburgh Penguins, heralded as among the most stunning in the Habs' 100-year history, sent tens of thousands of jubilant fans spilling into the downtown core Wednesday night in an ocean of red, white and blue.

Hours later the alcohol-fuelled remnants of that crowd began taunting Montreal police, tossing bottles at them and their horses. Then some covered their faces, smashed store windows and started looting.

Police regained control of the downtown early Thursday by charging into the mob, discharging tear gas and jabbing their batons into the ribs of any stragglers.

At least 25 people were arrested. Two officers suffered minor injuries.

The vandalism occurred after the Ste-Catherine Street area had already mostly emptied out, following a family-friendly scene where a little girl hoisted a makeshift Stanley Cup from atop her father's shoulders to the cheers of onlookers.

By around midnight, store windows were being smashed.

Looters concealed their faces -- in some cases with the garments they'd already stolen, not bothering to pluck away the price tags fluttering from their faces.

With their identities hidden they leaped through the broken storefront windows and emerged moments later with their arms full.

One man warned his lady friend, as they dashed away from a liquor store, to be careful with the loot.

"Hide the bottle," he snapped.

"The police."

He was referring to the line of officers who watched impassively from the closest street corner. They were waiting for the reinforcements on the way.

Suddenly, rows of black-clad riot cops charged in from the peripheries, rattling their shields as a warning to the crowd.

They began blasting tear-gas canisters into the mob. As people coughed and scurried away, the police followed; the slowpokes in the crowd were slammed repeatedly to prod them along. It made no difference whether they were looters or happy hockey fans in the wrong place. If they were there, they got hit often.

One man complained he'd had a tooth broken. Stragglers who paused and tried peacefully explaining why they needed to be there received the same reaction: a few swift, painful jabs in the torso.

Si Si Gow, a 19-year-old international student from China, walked around the area with her boyfriend afterward.

"I was at Crescent (Street) just now, which is really crowded and dirty with all the garbage that was thrown. I understand everyone is happy about what happened -- the victory -- but it's a little bit too much. Look at the street -- it's all messed up."

The evening began with a celebration that might be expected in a hockey-mad city, after its team squeaked into the playoffs before miraculously defeating two of hockey's best teams.

Tens of thousands of ecstatic Canadiens fans streamed into the streets to celebrate the team's elimination of the defending champion Penguins.

Fireworks erupted over Ste-Catherine Street as people crowd-surfed and held aloft trinkets including Stanley Cups and, in one case, a stuffed penguin.

Ronnie Cukier went downtown with his daughter and her friends because he wanted them to experience a true Montreal hockey celebration -- a rarity since the Habs delivered their last championship in 1993.

"We've been waiting for this Cup for a long time," Cukier said.

"I've seen a few already. But let the kids see a few of them. Now's our time. This is our year to win the Cup."

After upsetting two of the best teams in the league, the unheralded Habs have suddenly enjoyed their longest playoff run since that Cup win 17 years ago.

The city's beloved Habs were actually 750 kilometres away, disposing of the mighty Penguins in Pittsburgh with relative ease in Game 7 after trailing 3-2 in the series.

The impromptu block party kept growing, fed by the 21,000-odd fans who noisily spilled out from the Bell Centre after watching the 5-2 victory on a giant screen. The capacity crowd had snapped up tickets to see the game on the giant screen the instant they went on sale.

Fans cheered at each image of the puck being cleared from the Habs' zone. They roared every time it entered Penguins territory.

And the sight of Mike Cammalleri pumping his fist after a second-period goal literally prompted them to bow in the direction of his flickering, digitized likeness. They offered the same deferential cheer for goaltending hero Jaroslav Halak at game's end.

Their loudest boos? Those were triggered by the sight of superstar Sidney Crosby looking up from the ice to complain to the referees, pleading for a penalty after he was wrestled down.

People joyfully tossed Habs jerseys onto the ice surface in Montreal as the final buzzer sounded. They spilled out into the streets chanting, "Na na na, hey hey, goodbye," and "We want the Cup!"

Riot police smiled warily as they watched the post-game scene.

Montreal has a long history of hockey-related hooliganism.

Cars were burned and downtown stores were trashed and looted after the Canadiens beat the Boston Bruins in 2008 to advance to the next round of that season's playoffs.

There were also riots after Stanley Cup wins in 1986 and 1993.

The most famous riot occurred in 1955 when Habs legend Maurice Richard was suspended and fans took to the street to cause such havoc that "the Rocket" took to the airwaves to publicly plead for calm.

Police said hockey fans don't deserve the blame for any of the looting or vandalism after major Habs wins in recent years.

They say none of the people they arrested in 2008 had tickets to the game on them.

An area was set up Wednesday by the city for a tailgate party around the Bell Centre, with a DJ and refreshment stands. The goal was to keep hockey fans and potential looters separate.

Up next for the Canadiens in their first conference final since 1993 will be either the Boston Bruins or the Philadelphia Flyers, who play their Game 7 on Friday night.

Before Wednesday's events, the team had one message for Montrealers at a joint news conference with the local police earlier in the day: please behave.

"I know our fans will have fun but in respect and dignity," said Habs legend Rejean Houle, who also acted as team spokesman at the news conference.

He repeated his plea, in both French and English, on the arena's giant screen during the game. His message received cheers from the Bell Centre crowd, in both official languages.