Kris Lees' better judgment tells him Invincible Gem should be looking for a paddock and a decent rest.

Instead, the three-year-old filly continues to be one of the surprise packets in his stable and one of the most improved three-year-old fillies in Sydney racing.

And now she has some black type to go with her impressive run of form after a Group Three Spring Stakes romp at Randwick on Monday.

"She's just a plain-looking little filly but she's just gone to a whole new level this preparation," Lees said.

"I was looking for a reason to give her a break after her last win but she just thrived.

"And I said to the owners we've just got to have a throw at the stumps in a stakes race with her.

"She probably should be going for a break but it's hard to spell a filly when they are winning like that."

Invincible Gem, the $3.80 favourite, gave Lees a race-to-race training double after Le Romain's Southern Cross Stakes victory.

She raced clear to bring up a hat-trick of summer wins to beat Faraway Town ($7.50) by 3-3/4 lengths.

Winning jockey Brenton Avdulla said Invincible Gem's fitness edge over her rivals had cancelled out some concerns he had about the filly running out the 1600 metres.

"Kris has kept raising the bar with her and she's kept improving," Avdulla said.