Mark Winterbottom had hoped to walk away from Sydney Motorsport Park with the V8 Supercars championship lead back in his grasp.

Instead, he was left to rue a weekend of poor results and questioning whether even a top-three finish in the title race is still possible with five rounds remaining.

His below-par run culminated on Sunday when he copped a drive-through penalty for an opening-lap bump on Ford Performance Racing (FPR) teammate David Reynolds.

The 40-odd second trip down pitlane cost Winterbottom dearly, as did a damaged tyre which forced an unscheduled change in the closing stages.

The 33-year-old, who started from 15th, ended up finishing 20th.

Winterbottom said he was surprised by the penalty handed down by the stewards, having expected it to be reviewed post-race.

“There’s nothing you can say now that makes it go away, so you just cop it,” he told AAP.

“It was just a reaction to the incident, but they’re just doing their job.”

FPR boss Tim Edwards, however, was less forgiving.

“I disagree with it,” he told the Seven Network during the race.

“Yeah, of course, Mark hit him.

“… But it’s inexcusable to make a decision like that without all the facts.”

Winterbottom, who grew up just minutes from the Eastern Creek circuit, held the championship lead for more than three months until Jamie Whincup stole it from him last round at Ipswich.

While he remains in second place overall, a 15-point buffer has now blown out to 135 points. Whincup’s Red Bull Racing teammate Craig Lowndes is a further 78 points back.

“There’s no use worrying about the championship, to be honest,” Winterbottom said.

“If we keep doing the times we’re doing and running in the pack, we’re not going to win it.

“We need to work hard and make our cars quick again. We’re going to be lucky to finish top three the way we’re going.”