Ignacio Piatti and Anthony Jackson-Hamel scored braces as Montreal beat an understrength Toronto 5-3 in the 401 Derby at BMO Field.
Piatti was fortunate for the opener, blocking a clearance from goalkeeper Alex Bono and watching the ball find the back of the net.
It was 3-0 inside 25 minutes as Marco Donadel unleashed a 30-yard rocket and Piatti finished clinically from just inside the area.
A Deian Boldor own goal pulled one back for Toronto, who were without star duo Sebastian Giovinco and Jozy Altidore due to lower body injuries.
Jackson-Hamel struck a quick-fire brace shortly after the break and while Tosaint Ricketts netted twice late for Toronto, the visitors held on.
Despite just their fourth loss of the season, Toronto remain 11 points clear atop the Eastern Conference, while Montreal ended a four-match losing streak and stayed seventh.
In Atlanta, United crushed the LA Galaxy 4-0 to continue their goal scoring ways.
The in-form Josef Martinez tapped in his eighth goal in four games to open the scoring before Yamil Asad struck twice, firstly on the rebound and later tapping in a Hector Villalba pass.
Trailing 3-0 after 20 minutes, it got worse for the Galaxy as midfielder Jermaine Jones was sent off before halftime.
A chipped finish from Miguel Almiron extended Atlanta's lead prior to the break and while they had Brandon Vazquez sent off late, they climbed into fourth in the Eastern Conference.
Gerardo Martino's impressive side has now scored 17 goals in a four-match home stand.