Rinus van Kalmthout finished eleventh on Sunday at this weekend's second IndyCar race in Ohio.
The Dutchman was overtaken in the final lap by reigning champion Scott Dixon and crossed the finish line just outside the top ten.
Twenty-year-old Van Kalmthout, who started eleventh, battled into the top eight after a strong opening phase, but failed to hold onto that position.
After his pit stop, he lost several places and seemed to be heading for tenth place.
In the last lap Van Kalmthout was passed by championship leader Dixon, who had to catch up halfway through the race due to a spin.
The Hoofddorper kept the New Zealander behind him for a number of rounds, but had to give up his position in extremis.
Van Kalmthout, who finished eighth in the first race at Mid-Ohio on Saturday, was still the best rookie in eleventh place.
He increased his rookie championship lead over his main competitor Álex Palou, who failed to finish despite a fourth starting position.
Herta wins third race of IndyCar career
Victory at the Mid-Ohio Sports Car Course went to Colton Herta.
The 20-year-old American outperformed his fellow countrymen Alexander Rossi (second) and Ryan Hunter-Reay (third) and thus booked his third victory of his IndyCar career.
The IndyCar season continues on October 2 and 3, with races in Indiana.
Later that month, the season will close with a race in Florida.
See also: Van Kalmthout for the third time in a row in top ten at IndyCar Series