When people think of the rivalry between Toronto FC and the Montreal Impact, they tend to think about two Major League Soccer playoff series in the past two years and some insults traded via signs in the stands.

But Richard Legendre will tell you this competition, which rivals the much, much older Toronto Maple Leafs-Montreal Canadiens enmity when it comes to intensity, goes back further. That is why it is a real rivalry, what the executive vice-president of the Impact defines as "a natural rivalry."

"It's based on some epic games, historical moments throughout the last 10 years, even before Major League Soccer," Legendre said in advance of the first league game of the MLS season between the teams, at Montreal Stade Saputo on Sunday. "You know, if there is a rivalry and nothing happens in the rivalry it can fade away. But we went from historical game to historical game."

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Historical games for the current players and management of Toronto FC mean the MLS playoff games with the Impact dating to 2015 when the Montrealers embarrassed the Reds in their first playoff appearance. Then there was the epic Eastern Conference final last November when the Impact won the first game and then TFC came back to win the series with two extra-time goals in the second game.

Players, coaches and managers will tell you rivalries need intense playoff series to burn brightly. And Legendre speaks of playoff battles that go back to 2008 when TFC was in its second MLS season. At the time, the Impact was still in the second-tier United Soccer League and hoping to make the jump to MLS as an expansion team, which it accomplished in 2012.

On July 22, 2008, the Canadian Championship game, the winner of which would advance to the CONCACAF Champions League the following year, was played between the Reds and the upstart Impact at BMO Field. "To say we were not the favourite was an understatement. It was an amazing game," Legendre said.

The game ended 1-1, with the Impact just stopping a seemingly sure TFC goal near the end of the game. The tie gave the Impact the championship and the team went on to another improbable feat, getting as far as the quarter-finals of the CONCACAF Champions League. In 2009, TFC returned the favour. It played Montreal again in the Canadian Championship but needed to win by at least five goals to get the title. TFC humiliated the Impact 6-1 on its own field and as far as Legendre is concerned, the rivalry was in full swing.

While none of the current TFC players was around for those games, to a man they say the Impact is the team they want to beat more than any other.

"I've played in some big rivalries," said veteran TFC defender Drew Moor, a Dallas native whose antennae nonetheless is acute in his two years in Toronto. "I played in the FC Dallas-Houston rivalry and the Colorado-Salt Lake rivalry. But there's something different about this one.

"I can't put my finger on it. I think it's not just a rivalry in sports, it's a rivalry in politics, it's a rivalry in languages. You can just tell, maybe not that both cities hate each other, but both cities have something that I don't quite understand. It's almost an eerie feeling when I'm walking on the streets of Montreal and I pass some Impact fans."

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Add the elements of language, culture, an existing hockey rivalry and last year's epic MLS conference final with two large groups of passionate fans for both teams and it's no surprise the rivalry burns as hot as Leafs-Habs. But as Moor noted, there is more cheek than hate in the interaction between the Impact and TFC supporters groups despite the fact the Impact had to sanction some fans for a profane sign during the first game of the Eastern Conference final in 2016.

Some Impact fans held up a three-tiered sign before the first game of the series, which drew a crowd of 61,004 to Montreal's Olympic Stadium. The English translation of the sign was "What people think, we dare say aloud. F--- Toronto." The Impact went on to win 3-2.

The next week in Toronto, TFC supporters responded with their own sign: "We Dare Say What Everyone Thinks – Quebexit." TFC responded as well, scoring two goals in extra time to win the second game 5-2 and the series by a 7-5 aggregate score, which sent the sellout crowd of 36,000 at BMO Field into a frenzy. TFC gained another leg up on the rivalry in June when it beat the Impact in the Canadian Championship final, and it reigns in first place in the MLS this season while the Impact, thanks to a slow start, is fighting to get into a playoff spot.

But the Impact has its own MLS wins over TFC. In 2015, when TFC was supposed to be turning itself around, the Reds lost the last regular-season game to Montreal to give the Impact the home field for a sudden-death playoff game. This was the Reds' first playoff appearance since joining MLS in 2007 but a few days later they were humbled 3-0 by Montreal.

Before that game, TFC head coach Greg Vanney said, "I would have said from our perspective we wouldn't have looked at it as much of a rivalry yet. Then they knock us out and we feel an emotion of pure disappointment, embarrassment in some ways. Then the next year comes an epic series that knocks them out. Those type of things add to the [rivalry]."

While there is an intense mutual dislike on the part of the players – borne out by a physical Canadian championship series that left TFC defender Steven Beitashour seriously injured – there is respect on all levels, including management.

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"[Impact owner] Joey Saputo and I were chatting at the all-star game," TFC president Bill Manning said. "We were saying how we respect each other as franchises but we want to beat the hell out of each other.

"As franchises, we do work with them on some things, collectively our TV deals and sponsorships and stuff."

But the business deals are forgotten when the games start.

"If you're calling me and I don't have a story [about an epic game] then the rivalry falls flat," Legendre said. "That's not the case here. Almost every year there is something major happening between the teams – 2015 was amazing and 2016 was even more amazing.

"That keeps the fire burning."