As the race unravelled, Palou appeared to be the only challenger to Herta, but lapped traffic proved to be difficult to manage.
Despite finishing in second place, Palou has ensured he has placed one hand on the Astor Cup as he now leads his only challenger, Pato O’Ward, by 35 points with a maximum of 54 remaining.
Grosjean was one of the biggest movers of the race and claimed the final podium spot from 13th on the grid. The Frenchman even put a stunning pass on six-time series champion Scott Dixon at the Corkscrew early on.
While trying to chase down Palou, Grosjean did try another long-range lunge but made contact trying to lap Jimmie Johnson, but both carried on unscathed.
Graham Rahal was also another major mover in the race going from 12th to fourth.
O’Ward’s chances of a first IndyCar title slipped further after his No.5 Arrow McLaren SP car just couldn’t manage the tyres as well as his rivals.
A solid afternoon for Marcus Ericsson saw the Swede finish in sixth ahead of Josef Newgarden after a late-race battle.
Newgarden now requires a major fault for Palou at the season finale in Long Beach in order to clinch a third series title as he now sits 48 points behind.
Simon Pagenaud finished in eighth to ensure a second Penske car would finish inside the top 10.
A slow pit stop for Oliver Askew saw him lose ground after running higher up the order, but the Floridian still secured ninth place ahead of Ed Jones who rounded out the top 10.
The battle for Rookie of the Year honours will also go to the final round as 20 points now separate the two drivers thanks to Grosjean’s podium finish as Scott McLaughlin could only finish in 12th place.
The 2021 NTT IndyCar Series finale will take place on the famous streets of Long Beach on September 25-26.