Winx's younger sibling Covent Garden has been upstaged on debut at Canterbury, finishing unplaced in heavy conditions in a race won stylishly by another well-bred two-year-old.

Covent Garden, a half-sister to now-retired champion Winx, stepped out for her first start in Wednesday's Harry Angel @ Darley Handicap (1100m).

With Winx's jockey Hugh Bowman aboard, the Chris Waller-trained $4.40 second favourite never appeared comfortable in the heavy conditions and finished sixth of the seven runners, with debutant Sixgun storming home to register an impressive three-quarter length win over favourite Camerlengo.

Covent Garden is a daughter of Exceed And Excel out of Winx's dam Vegas Showgirl and is raced by her breeder John Camilleri, who also bred Winx.

The Waller-trained four-time Cox Plate winner Winx was retired last year after amassing 37 wins from her 43 starts including an unbeaten 33-race sequence spanning four years from 2015.

Sixgun is the younger brother of Group Two Arrowfield Sprint winning-colt Splintex and a half-brother to Group-placed mare Invictus Salute who, like Sixgun, are both trained by Mark Newnham.

Newnham says Sixgun is another nice horse from the family and was impressed by the way he got the job done on debut.

"He's probably a bit more physically developed than Splintex at the same stage but he's got a few wayward traits that Splintex didn't have," Newnham told Sky Thoroughbred Central.

"We've had to iron that out with a few trials and a change of gear. After his last trial we've put the cross-over noseband on him and that seems to have worked well."

Sixgun spotted most of his rivals a big start coming to the home turn but finished strongly under apprentice Robbie Dolan.

"I didn't think he would pick up and win like that," Dolan said.

"It's not that he wasn't going well he just didn't know what he was doing.

"It was his first time on a heavy track like that and it just took him a while to really balance up on it. But when he let down up the straight I was always confident I was going to win then.

"He's probably still not 100 per cent in the mind yet but for him to win like that first time in a race and with so much improvement left to come for him, he could be exciting."