Group One winner First Seal has shown her class in her Melbourne debut, delivering a special win for her connections in the Group Two Tristarc Stakes at Caulfield.

The John Thompson-trained mare stripped a fitter horse in Saturday's 1400m race than when she loomed up in the straight before finishing fifth in the Golden Pendant first-up in Sydney three weeks ago.

After settling midfield with cover, Blake Shinn had First Seal ($7.50) out in the clear in the straight and she let down powerfully to reel in the in-form favourite Tycoon Tara ($2.90) to win by a short neck.

First Seal, who has won six of her 17 starts with another six seconds, had the wood on Winx early in their three-year-old season, including when winning the Group One Flight Stakes in 2014.

"She's a lovely mare. She was the best horse in the race today, she just needed to handle Caulfield. She wobbled a little bit around the corner but class prevailed," Thompson said.

"Look, the days of beating Winx are a long time ago. She's had a lot of injuries, nothing major but just little niggles and it's good to see her come back and win. I'm sure she's got more wins in her.

"She's a special horse to me and the stable."

The Group One Myer Classic (1600m) in two weeks at Flemington is First Seal's main spring target.