Craig Lowndes has been hit by his team and the stewards as he endures a tough day at Symmons Plains.

In race one, the V8 Supercars championship and race leader was hit by his team-mate Jamie Whincup in a robust overtaking move, losing the lead and eventually finishing eighth.

A stewards inquiry has also ruled Lowndes must start from the back of the grid after tape was found over a hole his car’s rear window during qualifying.

The penalty was applied because the tape constituted a safety issue, and gave Lowndes an slight aerodynamic advantage.

It’s far cry from the veteran Red Bull racer’s outlook half-way through race one when he led the race and was looking forward to a second front row start in race two.

The twin blows are likely to shave Lowndes’ championship lead by the end of the day.

Whincup said the pair’s bump was “unfortunate” but he had no regrets over his passing move.

“I feel like I haven’t done anything wrong,” he said.

“We’ve been mates for ten years and hopefully that can continue.”

Team owner Roland Dane struggled to hide his frustration at the situation.

“I can sympathise with both of them, I’m just annoying it’s between both our cars,” he said.

“They know not to do that and it’s won’t be happening again.”

Stewards are yet to rule on the legality of Whincup’s passing move but have announced an investigation.

James Courtney placed second in race one with Ford’s Mark Winterbottom third.

Russell Ingall, who qualified third fastest, held off Volvo’s Scott McLaughlin for fourth place around the Symmons Plains circuit.

Saturday’s second race begins at 4:35pm (AEDT).