But not as high as when Nelsen's Blackburn Rovers played nearby Burnley.
"The most intense game I've ever experienced," Nelsen said Tuesday of the Lancashire matchup between the northwest English neighbours. "I've experienced Tottenham-Arsenal but it was nowhere near the Blackburn-Burnley one. There's a real hatred there."
Nelsen recalled how a female police officer was knocked out by a Burnley fan who had invaded the field hoping to get a piece of Blackburn midfielder Robbie Savage. That 2005 FA Cup meeting also saw a breakdancing male streaker and a coin thrown at a Burnley player, even though there were 600 police on duty.
"It's absolutely huge," Nelsen said Tuesday of the Blackburn-Burnley rivalry. "It's way bigger than most people know in England."
Nelsen gets a taste of the Toronto-Montreal rivalry on Wednesday as the two meet in the first leg of the Canadian Championship semifinal.
It should be a picnic compared to the so-called "cotton mill derby" of Blackburn-Burnley.
Asked to compare the rivalry with that of the Wallabies-All Blacks rugby Test matches, the New Zealand-born Nelsen told the Guardian newspaper in 2009 that the Australia-New Zealand rugby rivalry was "an absolute yawn festival" in comparison.
The games were rare when Nelson played for Blackburn, which could look down at Burnley from the Premier League. But now both are in the second-tier Football Championship.
The hatred still exists between the two.
"Police warning over Blackburn Rovers v Burnley FC clash" was last month's headline in the Burnley News ahead of the 1-1 tie between the clubs.
A "major policing operation" was promised, with 4,000 Burnley fans told to meet at their stadium at 9:45 a.m. so they could bus to Blackburn.
The same thing happened in 2009 with the Guardian reporting that all 3,000 Burnley fans with tickets to the match at Blackburn's Ewood Park had been ordered to show up at Burnley's Turf Moor stadium at 9:15 a.m. so they could make the 14-mile (22.5-kilometre) journey in a convoy of buses.
That included the poor Burnley season-ticket holder who lived four minutes from the Blackburn stadium.
You can dial down the venom for Toronto and Montreal, although TFC players will remember that Montreal won 2-1 March 16 in MLS play at Olympic Stadium.
With the teams facing a crowded schedule, Toronto and Montreal will both be looking to showcase the depth in their squads Wednesday.
The Impact have had the last 10 days off but face six games in the next 18 starting Wednesday at BMO Field. Toronto gave up a stoppage-time goal in a 1-1 tie with the visiting Houston Dynamo in MLS play Saturday, the opening of their stretch of six games in 18 days.
Montreal (4-1-1) says backup Evan Bush will start in goal at BMO Field while newly signed Italian forward Daniele Paponi is eligible to play. Defender Matteo Ferrari stayed at home with a calf injury.
Nelsen confirmed Tuesday that goalkeeper Stefan Frei will lead out his team against Montreal, meaning nights off for both No. 1 'keeper Joe Bendik and defender-skipper Darren O'Dea.
"We know we have a heavy fixture list coming up," Nelsen said after practice Tuesday. "So yes, of course, the squad's going to be used to its capacity."
Midfielders Reggie Lambe and Jeremy Hall and striker Robert Earnshaw are also expected to be given a rest. Defenders Logan Emory (ankle) and Darrel Russell and Richard Eckersley (both hamstring) are doubtful.
Ashtone Morgan, Danny Califf, Gale Agbossoumonde and Ryan Richter are likely to see action on the backline for Toronto (1-2-4) with the likes of Kyle Bekker, John Bostock and Jonathan Osorio getting their chance in midfield.
Andrew Wiedeman could get his first start up front this season.
FC Edmonton of the North American Soccer League hosts the Vancouver Whitecaps at Commonwealth Stadium in the other semifinal Wednesday.
The second legs are slated for May 1 in Montreal and Vancouver with the final set for May 15 and 29.
The tournament winner will represent Canada in the 2013-14 CONCACAF Champions League.
Montreal won the inaugural Canadian championship in 2008, with Toronto winning from 2009 to 2012.
The Impact have never beaten TFC in Canadian Championship play, losing six games and tying two. Last season, Toronto won 2-0 at home and tied 0-0 at Montreal in the tournament.
In league play Saturday Toronto hosts the New York Red Bulls while the Impact entertain the Chicago Fire at Stade Saputo.