The latest success means Dixon now matches Mario Andretti in second on the all-time IndyCar winners list.
From the start, polesitter Herta was unthreatened, while Dixon swept across from the outside to ensure Newgarden couldn’t sneak up from third to claim second.
Newgarden checked his momentum and that allowed Alexander Rossi around his outside to try and claim third, but Newgarden had put the matter beyond dispute by the end of the lap.
Scott McLaughlin, his Penske team-mate, passed David Malukas for fifth, but there was even worse luck for the other Dale Coyne Racing entry of Takuma Sato, who was shoved into the wall at the Turn 1 kerfuffle, and limped his very broken car back to the pits. The debris left behind obliged race control to throw the full-course caution.
With defending champion Alex Palou - starting down in 22nd - and Will Power among the drivers to make early pit visits on an alternate strategy a few laps after the restart, the leaders soon started to head in.
Newgarden remained ahead of Rossi but were now split by rookie Malukas. Herta stopped on lap 19, a tour after Dixon and found himself being outbraked by the six-time champion into Turn 1, to effectively take the lead.
Behind them, Newgarden and now Rossi were ahead of Malukas, while Felix Rosenqvist had turned in fast enough laps at the end of his stint to emerge ahead of McLaughlin and hold off the Penske driver.
However, Dixon wasn’t yet in the lead, for Graham Rahal, Rinus VeeKay, Pato O’Ward, Jimmie Johnson and Conor Daly had risked running a long first stint on their primaries to try and make a net gain.
By the time the majority of these had finally stopped, Dixon was out front with a 2.5-second lead over Herta, the pair of them in a race of their own.
A further 14s behind them, Daly continued to hold up a train of cars led by Newgarden, Rossi and Rosenqvist, before Daly uncorked the bottle on lap 36 and pitted.
Not that Newgarden then made any notable progress thereafter because he was in fuel-save mode having been one of the early stoppers.
Behind, Rossi and Rosenqvist had begun fighting over fourth - and that dispute ended in tears on Lap 45, just as Rosenqvist was encouraged by his strategist to make the pass.
At Turn 3, the AMSP driver flicked to the inside of future AMSP driver Rossi, and he was fully alongside as they exited the turn but, as Rosenqvist floored the throttle, his car slid sideways and the contact sent the Andretti car hard into the wall.
The drivers wended their way into the tortuous pitlane, and Newgarden suffered a horrible stop as he stopped too far from his crew, and the refueller struggled to get the nozzle engaged, leaving Newgarden down in 11th.
With VeeKay and Daly having stayed out front after their late stops, Ed Carpenter Racing had a 1-2 ahead of Dixon, Herta, Rosenqvist and McLaughlin.
Herta was now fully able to stay in Dixon’s wake, but then the yellow flew for debris at Turn 1 – concrete debris, caused by the track breaking up – compressed the field once more, and a subsequent yellow for clash between Kyle Kirkwood and Johnson led to VeeKay pitting and Dixon regaining the lead.
The next restart came at the end of lap 66, with 19 laps to go, and into Turn 1, Rahal muscled down the inside of McLaughlin to snatch fourth and the Penske driver got out on the marbles through Turn 2 and lost a handful of other places.
Up front, Dixon pulled away from Herta, who was having to watch his mirrors for Rosenqvist, but the Swede couldn’t quite complete the move, and fell half a second short.
Ahead of them, Dixon scored his first win of the year, after leading 40 of the 85 laps, and ensuring he has now scored at least one win in 18 seasons.
Rahal was a great fourth ahead of Marcus Ericsson, while Palou can be proud of his charge from 22nd to sixth place.
Christian Lundgaard was a fine eighth ahead of Penske's McLaughlin and Newgarden, who completed the top 10.
IndyCar Toronto Race Result (85 laps):
