Having fended off threats from Palou and Grosjean, the Penske driver took the team’s third consecutive win after a crash-strewn race.
It marked Newgarden’s 22nd career victory, equaling Tony Bettenhausen and Emerson Fittipaldi in the record books.
Former Formula 1 driver Grosjean took his second series podium, having been denied pole for Sunday’s race after a crash in qualifying, while Palou took third place for Chip Ganassi Racing.
Having started in second, Newgarden was left trailing by the Andretti Autosport polesitter’s perfect start and was forced to fend off Palou in the opening stages.
The trio ran out front for much of the distance, with Palou leading from Newgarden and Herta after pitting early.
But a crash from Herta at Turn 9 on an in-lap, leaving him in the outside wall, coupled with a cleverly timed pitstop put Newgarden into the lead with 19 laps remaining.
Romain Grosjean, Andretti Autosport Honda
Photo by: Jake Galstad / Motorsport Images
At the restart, Newgarden held off Palou, but behind them, Palou’s team-mate Marcus Ericsson lost the rear of his car out of Turn 4, tagging the wall with his left rear.
Grosjean and Will Power (Team Penske) ducked through, but as Ericsson pulled over to the right to park it on the inside of Turn 5, Scott Dixon ran into the back of him, which allowed Arrow McLaren SP’s Pato O’Ward to slip past the six-time champion, although Dixon escaped without damage.
Grosjean, on alternates, then attempted to pass the Chip Ganassi Racing driver for second into Turn 1 on Lap 69.
Though that attempt failed, the Andretti driver repeated the effort on Lap 70, and this time he was further ahead into the brake zone, and was able to carve across and claim second.
Grosjean immediately started applying the pressure on Newgarden, who was looking scrappy in defence, but the Frenchman ran out of push-to-pass boost.
Alex Palou, Chip Ganassi Racing Honda
Photo by: Michael L. Levitt / Motorsport Images
However, he would get another chance at tackling Newgarden (who had 4sec P2P left) as Jimmie Johnson’s torrid weekend finished slightly early after sliding his Chip Ganassi car into the Turn 8 tyres, and being collected by David Malukas of Dale Coyne Racing.
The restart with four laps to go saw Grosjean try to make the pass into Turn 1, but Newgarden’s defence on the inside line was enough to rebuff him.
A lap later, Newgarden used his last spurt of P2P to launch off the hairpin, and he was effectively safe for another lap.
He also remained ahead without an apparent threat from Grosjean on the penultimate lap, and then the yellow had to come out when Sato slid into the tyres in Turn 8 and couldn’t restart.
Palou held on to finish third, with Power in fourth to put himself over the 100-point barrier in the standings.