Scott Dixon’s poor result at Monday's Iowa Corn 300 has seen his IndyCar Championship lead shrink to 33 points.
The Kiwi driver finished 12th after a tough race that saw him struggle for pace, as he dropped two laps behind the leader on the opening stint around the short oval track.
Dixon and his team changed strategy mid-race in an attempt to get back on the lead lap, but his car wasn't up to it and he finished four laps behind race winner James Hinchcliffe.
The 37-year-old's problems became worse when his crew put the wrong tyres on late in the race, causing Dixon to make an extra stop to rectify the mistake.
"The first stint, I think it was all round grip, it was really loose," Dixon explained.
"It got better through the race, but then we had a shifting over-heating issue, where we could only use one gear at a time, let it cool off and then go back.
"That definitely hampered us."
A late yellow flag helped minimise the damage though, as his championship rivals failed to fully capitalise on Dixon's rare off-day.
Josef Newgarden dominated the race and looked on track to cut the Kiwi's lead to less than 20-points, but he was hampered by the caution, as his team decided to dive into the pits for fresh tyres.
Hinchcliffe was the main benefactor, as the race was never restarted and finished under the yellow flag, with Newgarden coming home fourth.
"We had a great car today, so I can't complain much," Newgarden said. "It is a tough pill to swallow, seeing Hinch go past me at the end. It just went away from us."
The series moves to Toronto next week – a circuit where Newgarden has won two of the last three races.