The Penske-Chevrolet driver lapped the very ‘green’ track in 61.1211sec, an average speed of 105.194mph to eclipse teammates Josef Newgarden and Simon Pagenaud.

Chip Ganassi Racing-Honda’s Scott Dixon, who narrowly edged Castroneves for pole here last year, was fourth fastest, almost 0.6sec adrift of the Brazilian and about a tenth clear of Rahal Letterman Lanigan Racing-Honda’s Graham Rahal.

Spencer Pigot was a highly impressive sixth in the Ed Carpenter Racing-Chevrolet, ahead of Schmidt Peterson Motorsports-Honda’s James Hinchcliffe and Tony Kanaan in the second Ganassi.

Andretti Autosport’s Ryan Hunter-Reay and Takuma Sato completed the top 10.

Marco Andretti was 11th and might have been far higher, but completed only 11 laps before his car developed a major oil leak.

The fourth Penske of Will Power, who has three Toronto wins to his name, was only 16th and he was one of many drivers to take to the runoff areas.

Another was Sebastian Saavedra, replacing Mikhail Aleshin in the #7 SPM-Honda this weekend. Despite completing the most laps of any driver in the session (27), the Colombian was unsurprisingly slowest by a full second.

Practice results:

Pos.	#	Driver	Time	Gap
1	3	Helio Castroneves	1'01.1211
2	2	Josef Newgarden	1'01.5098	0.3887
3	1	Simon Pagenaud	1'01.5445	0.4234
4	9	Scott Dixon	1'01.7040	0.5829
5	15	Graham Rahal	1'01.7236	0.6025
6	20	Spencer Pigot	1'01.7866	0.6655
7	5	James Hinchcliffe	1'01.8453	0.7242
8	10	Tony Kanaan	1'01.9580	0.8369
9	28	Ryan Hunter-Reay	1'02.0204	0.8993
10	26	Takuma Sato	1'02.0241	0.9030
11	27	Marco Andretti	1'02.0314	0.9103
12	19	Ed Jones	1'02.0934	0.9723
13	14	Carlos Munoz	1'02.0962	0.9751
14	8	Max Chilton	1'02.1024	0.9813
15	21	J.R. Hildebrand	1'02.1078	0.9867
16	12	Will Power	1'02.2245	1.1034
17	18	Esteban Gutierrez	1'02.2714	1.1503
18	98	Alexander Rossi	1'02.2913	1.1702
19	4	Conor Daly	1'02.8188	1.6977
20	83	Charlie Kimball	1'02.8693	1.7482
21	7	Sebastian Saavedra	1'03.9240	2.8029