Alex Palou says two costly mistakes are “unacceptable” after his IndyCar points lead was almost halved at Iowa Speedway.

The Chip Ganassi Racing driver was running third in the Hy-Vee Homefront 250 when he stalled during the first round of pit stops.

The two-time series winner had been running third at the time behind Andretti Global’s Colton Herta and Scott McLaughlin of Team Penske.

That dropped Palou down the order and as he sought to recover places the Spaniard spun on his own coming onto the front straight.

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Heavy damage to the #10 ruled him out of the contest and marked just his seventh DNF in four-and-a-half IndyCar seasons.

“I think I just lost it out of [turn] four,” said Palou.

“Driving mistake. There is no reason why. Just trying to recover from another driver mistake I had in the pits. Unacceptable. I’m very sorry for the #10 car.

“The car was good, it just wasn’t our day.”

Around goes the championship leader!@AlexPalou spins into the wall!

📺: #INDYCARatIowa on CNBC and Peacock pic.twitter.com/2UgN2eMulS

— NTT INDYCAR SERIES (@IndyCar) July 14, 2024

Palou came into Iowa on 329 points and only increased that to 336 after the first leg of the double-header.

Will Power was second in the points but fell to third after a torrid 250 laps in which he was penalised for speeding on pit lane before a late clash with Pietro Fittipaldi and Ed Carpenter.

Pato O’Ward rose to second in the standings after finishing runner-up to race winner Scott McLaughlin.

Palou’s advantage now stands at only 37 points over O’Ward while Power is 43 points in arrears in third.

Palou’s teammate Scott Dixon still holds down fourth, albeit just 46 points behind while McLaughlin’s win vaults him up to fifth. He trails by 59 points with seven races remaining.

The second leg of the Iowa Speedway double-header gets underway on Monday (AEST) at 2:30am.

IndyCar Series standings (after race 10 of 17):