A clash with Winx awaits Black Heart Bart after he emphatically answered distance doubts with a commanding win in the Underwood Stakes.

And Black Heart Bart's jockey Brad Rawiller, who rode with a calf injury after a barrier mishap at Caulfield on Saturday, can't wait to take on Australia's best racehorse in the Caulfield Stakes and the WS Cox Plate.

"We certainly had our confidence coming into today and it just backs our confidence up," Rawiller said after Black Heart Bart's 2-1/2-length win over 1800m.

"We're not going to be shying away from Winx, but at the same time you respect that she's a star. I'm pretty happy with how he was today in himself. Bring it on, I can't wait."

Trainer Darren Weir has put Black Heart Bart on a path to the Cox Plate and that goal will get its sternest examination in the Caulfield Stakes on October 8 when he faces Winx.

Black Heart Bart ($2.20) notched his second Group One this spring, sitting third behind leader The Cleaner until moving up to be in the position to pounce at the top of the straight.

He drew clear over the final 200m to beat He Or She, with Queen Elizabeth Stakes winner Lucia Valentina closing late to finish another half-head away.

Weir brought up his third Group One win this season in Melbourne and said it was good to see Black Heart Bart ran strongly through the line after his last-start second to Palentino in the Makybe Diva Stakes.

Saturday's win was Black Heart Bart's first victory beyond 1400m.

"I never had any doubts about the 1800 metres," Weir said.

"Obviously the opposition is going to get stronger as you head towards the Cox Plate, so he needs to be running like he did today to be thinking you're going to be competitive with them."

Black Heart Bart firmed from $21 to $13 for the Cox Plate behind Winx ($1.85), Hartnell ($8) and The United States ($9).

"She's the best horse in the country, but he's in the right shape now," Weir said.

"It will be a great clash. She's probably too good, but you never know.

"We've been a bit harder on him between last start and today and he's come on well. That will have him right up to the mark now."