Australia's Will Power was in apologetic mood after his second run-in with Kiwi driver Scott Dixon in as many weeks at the Indycar Grand Prix of Baltimore.
Power's car swerved right in front of Dixon during a restart and both hit the wall, ruining their hopes in a crash-marred race where almost every car in the 24-strong field sustained some kind of damage.
Power made it to the pit, but he was given a penalty for interference and finished 18th, one spot ahead of Dixon who was unable to continue.
The Baltimore incident came a week after Power's first win of the year at Sonoma, California, was soured when Dixon accused one of the Queenslander's pit crew of gamesmanship.
The New Zealander lost the lead late in the race after sustaining a drive-through penalty for clipping a tyre held by the crew man and sending him sprawling as he exited pitlane.
Power was more than willing to hold up his hand following Sunday's (Monday AM AEST) incident on Baltimore's street circuit however.
"I feel really bad,'' said Power said.
"I really had no idea that Dixon was there. I actually didn't even know until I got back to the pits and they told me.
"I feel terrible for him and his team. All I can do is tell them how sorry I am and move on to Houston.''
A furious Dixon, who entered the race 39 points behind series leader Helio Castroneves, now trails by 49 after the Brazilian limped home in ninth.
"That restart near the end was a complete botch,'' Dixon said.
"On the restart I had an overtake advantage on Power, it must have been in fourth-gear, so they can't complain about wheel spin.
"Then I got beside him and he ran me straight into the wall.''
France's Simon Pagenaud was the eventual race winner, his second victory of the year moving him to third on the standings behind Dixon.
Josef Newgarden was second, the best finish of his career, and Sebastien Bourdais took third.
Tony Kanaan, the Indianapolis 500 winner, made IndyCar history by participating in his 212th consecutive race. He eclipsed the mark held by Jimmy Vasser while driving in the No. 11 Chevrolet for Vasser's KV Racing team. Kanaan hit the wall near the end of the race and finished 15th.