BOSTON -- While some of his Yankee teammates were out enjoying a crisp Massachusetts morning, fifth starter Phil Hughes was on a mound in Florida, continuing to tune up for the regular season on Monday.

The 23-year-old right-hander threw the equivalent of 8 1/3 scoreless innings under simulated conditions at the club's Himes Avenue Minor League complex in Tampa, Fla., telling The Associated Press that he was "very happy" with the results.

Pitching against an arrangement of Yankees extended spring prospects without fielders present, Hughes was scheduled to throw six innings but needed to face more hitters because he was so efficient. Hughes struck out 12, scattered three hits and threw 70 of 100 pitches for strikes.

Because of early off-days on the Yankees' schedule, Hughes is not scheduled to make his regular-season debut until April 15 against the Angels. He departed Tampa immediately after his simulated game to join the Yankees in Boston for Tuesday's contest.

Hughes has a little more Florida baseball left to pitch. When the Yankees visit the Rays this weekend at Tropicana Field, Hughes is slated to make his final preseason mound appearance Saturday with the extended spring team.

"It gives me time to work on some more things -- basically like two extra spring starts," Hughes said when the plan was announced. "It'll be fine. I'm looking forward to the 15th. It's the first step of this year, and I'm looking forward to starting off well and keeping it going."

Hughes gave up 10 earned runs in 20 2/3 Grapefruit League innings (4.35 ERA), beating out Joba Chamberlain, Alfredo Aceves, Sergio Mitre and the since-released Chad Gaudin to serve as New York's fifth starter.

Yankees manager Joe Girardi has said that Hughes' improved changeup was a major plus in his favor, adding to his fastball, cutter and curveball.

"I don't think I'm done working on it," Hughes said. "It's never a finished process. I still feel like I can mature and throw my pitches in different scenarios, different counts. Now, with four pitches, I can really pitch."

A first-round selection of the Yankees in the June 2004 First-Year Player Draft, Hughes went 8-3 with a 3.03 ERA in 51 games (seven starts) in 2009, playing a key setup role out of the bullpen down the stretch. He sports a 5.22 ERA in 28 starts and a 1.40 ERA in 44 relief appearances.