Colton Herta topped an ultra competitive second Practice session at Toronto for Andretti Autosport ahead of Marcus Ericsson and Will Power.
Josef Newgarden and Alex Palou hit problems in an agonising session for that particular duo of championship contenders in Canada.
New Zealander Scott McLaughlin and 20-year-old Christian Lundgaard rounded out the top five as the first five were separated by just 3 tenths of a second.
The start of Practice 2 was delayed due to a plethora incidents earlier in the day in other series as track repairs occurred.
After a lengthy delay the session got underway a flurry of cars left the pit lane of the Primary Firestone tyres. Herta lit up the timing screens and went quickest for Andretti Autosport with a 1:01.5123.
Swedish driver Felix Rosenqvist locked up into Turn 3 in the early stages but kept his Arrow McLaren SP car out of the barriers and managed to continue.
Penske hit trouble as Newgarden had to cut his session short with mechanical trouble. Reigning champion Palou clattered the barrier, damaging his left front suspension as two championship contenders suffered problems early on in Practice 2.
The times quickly began to tumble as David Malukas broke the 1:01 barrier setting a 1:00.6834. He sat atop the timesheets ahead of Alex Rossi and Scott Dixon with half an hour to go for Dale Coyne racing.
Romain Grosjean went down one of Toronto’s many escape roads and recovered from a lock up as he sat fourth in the session with a 1:00.9964.
The Frenchman’s day got drastically worse as the former Formula 1 driver hammered the barrier at Turn 11 causing a puncture, bringing out the red flags.
Practice 2 resumed with 28 minutes left on the clock, Malukas was usurped by Herta with a 1:00.4871 as the track continued to rubber up.
New Zealander Dixon set the fastest time with 12 minutes remaining for Chip Ganassi Racing fractionally ahead of the Herta’s number 26 car in a very strong session.
The championship leader and Indy 500 winner Ericsson delivered a quiet session and sat in sixth place just four tenths behind Dixon in P1.
British driver Callum Ilott made up for lost track time after a crash in Practice 1 driving a clean session and ended up in P15 for Juncos Hollinger Racing. He set a best time of 1:00.9380 during his first visit to Toronto.
McLaughlin went to the top of the times with a 1:00.3389 for Penske ahead of Ericsson with just a few minutes left.
The Swede raised the benchmark and bested McLaughlin’s time. The times continued to get quicker as Herta went quickest with an impressive 1:00.0471.
Japanese driver Takuma Sato made contact with the barrier ending his session and causing a red flag with under a minute to go.
Practice 2 resumed with 51 seconds left, three cars joined the track but couldn’t do a flying lap as insufficient time remained at the end of the session.