The 23-year-old Californian set the tone early with a flying lap of 1m07.5382s around the 11-turn, 2.238-mile natural terrain road course.
His fastest time was achieved on a set of the harder primary tire compound.
Behind the Andretti Autosport pacesetter and two-time Laguna Seca race winner was Arrow McLaren’s Pato O’Ward, who trailed by 0.0529s, and was ahead of team-mate Alexander Rossi in third. O’Ward logged 33 laps, the most in the session.
Marcus Ericsson’s final race weekend with Chip Ganassi Racing saw him fourth on the leaderboard, 0.2531s off the top spot. Andretti’s Kyle Kirkwood finished up fifth.
Rahal Letterman Lanigan Racing was represented in sixth and seventh, led by rookie Juri Vips ahead of team-mate Graham Rahal. Juncos Hollinger Racing was represented in the top 10 with Callum Ilott in eighth.
Six-time IndyCar Series champion Scott Dixon came away ninth, with Ed Carpenter Racing’s Rinus Veekay rounding out the rest of the top 10.
Although the opening 30 minutes were uninterrupted, the rest of the 1h15m practice was plagued by stoppages with no less than five red flags.
It began with Romain Grosjean backing his Andretti Autosport machine into the tire barrier in Turn 4. The damage was significant as he was forced to climb out as his Honda was towed back to the paddock.
After a red flag that lasted just over 10 minutes, it took just another 180 seconds before Vips received an urgent radio message to stop the car due to an apparent engine issue. The Estonian stopped on the Rahal straight and was assisted by the safety crew, which towed him to the top of the Corkscrew, allowing him to coast back to pit lane on the downhill run in neutral.
Team Penske’s Scott McLaughlin brought out another stoppage following the next restart, losing the rear entering Turn 1 and ending up stuck in the gravel.
Another restart came and went briefly when Juncos Hollinger Racing rookie Agustin Canapino’s off course excursion that left him stalled in Turn 6.
The theme continued with Will Power, who led testing on Thursday, closing out practice with a fifth red flag after heavy contact with the barrier in Turn 4 and he stopped on course in Turn 5. The Aussie ended 13th on the timesheets. “I damaged the floor, man,” called Power over the radio.
Ahead of practice, IndyCar Officials slapped Canapino with a six-position starting grid penalty for Sunday’s Grand Prix of Monterey due to an unapproved engine change following the last round at Portland International Raceway.
| Cla | Nº | Driver | Car / Engine | Time | Delay | Laps |
| 1 | 26 | Colton Herta | Dallara/Honda | 1'07.5382 | 15 | |
| 2 | 5 | Patricio O'Ward | Dallara/Chevrolet | 1'07.5911 | 0.0529 | 33 |
| 3 | 7 | Alexander Rossi | Dallara/Chevrolet | 1'07.6336 | 0.0954 | 28 |
| 4 | 8 | Marcus Ericsson | Dallara/Honda | 1'07.7913 | 0.2531 | 18 |
| 5 | 27 | Kyle Kirkwood | Dallara/Honda | 1'07.8502 | 0.3120 | 20 |
| 6 | 30 | Jüri Vips | Dallara/Honda | 1'07.9175 | 0.3793 | 23 |
| 7 | 15 | Graham Rahal | Dallara/Honda | 1'07.9515 | 0.4133 | 26 |
| 8 | 77 | Callum Ilott | Dallara/Chevrolet | 1'07.9552 | 0.4170 | 25 |
| 9 | 9 | Scott Dixon | Dallara/Honda | 1'07.9676 | 0.4294 | 16 |
| 10 | 21 | R.van Kalmthout | Dallara/Chevrolet | 1'08.0553 | 0.5171 | 22 |
| 11 | 60 | Tom Blomqvist | Dallara/Honda | 1'08.0666 | 0.5284 | 26 |
| 12 | 10 | Alex Palou | Dallara/Honda | 1'08.0687 | 0.5305 | 16 |
| 13 | 12 | Will Power | Dallara/Chevrolet | 1'08.1056 | 0.5674 | 19 |
| 14 | 20 | Ryan Hunter-Reay | Dallara/Chevrolet | 1'08.1431 | 0.6049 | 22 |
| 15 | 18 | David Malukas | Dallara/Honda | 1'08.1797 | 0.6415 | 26 |
| 16 | 3 | Scott McLaughlin | Dallara/Chevrolet | 1'08.1919 | 0.6537 | 16 |
| 17 | 14 | Santino Ferrucci | Dallara/Chevrolet | 1'08.2098 | 0.6716 | 21 |
| 18 | 28 | Romain Grosjean | Dallara/Honda | 1'08.2391 | 0.7009 | 13 |
| 19 | 6 | Felix Rosenqvist | Dallara/Chevrolet | 1'08.2470 | 0.7088 | 25 |
| 20 | 2 | Josef Newgarden | Dallara/Chevrolet | 1'08.3103 | 0.7721 | 23 |
| 21 | 11 | Marcus Armstrong | Dallara/Honda | 1'08.3180 | 0.7798 | 21 |
| 22 | 55 | B.Pedersen | Dallara/Chevrolet | 1'08.3607 | 0.8225 | 29 |
| 23 | 29 | D.Defrancesco | Dallara/Honda | 1'08.4537 | 0.9155 | 24 |
| 24 | 06 | H.Castroneves | Dallara/Honda | 1'08.5527 | 1.0145 | 22 |
| 25 | 45 | C.Lundgaard | Dallara/Honda | 1'08.5958 | 1.0576 | 27 |
| 26 | 78 | Agustín Canapino | Dallara/Chevrolet | 1'08.7977 | 1.2595 | 19 |
| 27 | 51 | Sting Ray Robb | Dallara/Honda | 1'09.0907 | 1.5525 | 21 |
