ST. PETERSBURG, FLA. – Tyler Duffey throws his curveball like he's been doing it all his life. Not quite.

When Duffey started playing baseball, his father, Tim, would not allow him to throw the pitch, preferring his son develop a changeup.

Duffey picked up the curveball in high school, learning its nuances from Nathan Mitchell, a fellow Houston native who pitched in the Cubs organization.

"I've thrown the same one since Day 1," Duffey said. "I have not changed the grip, Something clicked and it just worked."

Duffey and his curveball will make their fourth appearance for the Twins on Wednesday against the Rays. After a forgettable major league debut Aug. 5 in Toronto, Duffey won his next two starts, giving up two earned runs over 13â…” innings.

But advance scouts are on the prowl, trying to find ways to attack Duffey. The rookie is ready. He can throw his curveball at different speeds and use his trusty changeup when needed.

Duffey

"That's been my game since forever," Duffey said. "l don't know if it is something I do that is different than everybody else. I try to spot up with it and not just throw it. I can throw inside or outside or down. I use it different ways."

That time of year

Conversations are ongoing about which minor leaguers deserve to be September call-ups.

Twins General Manager Terry Ryan visited Class AA Chattanooga last week and will spend time this week at Class AAA Rochester to evaluate players who could be brought up when rosters can expand Sept. 1 to include any player on the 40-man roster. That could be tricky for Chattanooga, which is headed to the postseason. Rochester is on the fringe of the wild-card race.

"I plan to, either [Wednesday] or Thursday, have a session with the guys here to talk about anybody's input in terms of areas we can fill needs or add depth or protect ourselves the best way we can as we enter the final month," Twins manager Paul Molitor said.

Relievers Michael Tonkin, Aaron Thompson and A.J. Achter could be call-up candidates. And the Twins always want an extra catcher, so Eric Fryer has a chance.

Slugger Kennys Vargas, Molitor said, has had consistently good at-bats, which helps his cause. Oswaldo Arcia has been terrible of late.

Top starting prospect Jose Berrios could run into an innings crunch. He pirched 139 ⅔ innings last season. The Twins don't want to increase a pitcher's workload more than 20 innings, so 160 would be his cap. Berrios has thrown 148 ⅓ innings between Rochester and Chattanooga.

The Twins also are finalizing rosters for the Arizona Fall League and offseason instructional league.

Etc.

• Tommy Milone, who got his first career save Sunday as an emergency closer against Baltimore, threw a light bullpen and will start Thursday.

• Former Twins righthander Brad Radke, who lives in Tampa, visited with former teammates Joe Mauer, Torii Hunter and Eddie Guardado during the off day Monday.

• Righthander Phil Hughes (sore lower back) is feeling better and will play catch Wednesday.

• Outfielder Aaron Hicks (left hamstring) is doing light jogging and hitting in the batting cage.

• Starter Ricky Nolasco (right ankle surgery) played catch Monday and did some light jogging Tuesday.