Jackson, 23, has pitched well this spring in compiling an 0-1 record with a 1.84 ERA in six appearances. With the off-day next Tuesday, the Rays will use their first four starters before starting again with Scott Kazmir and working through to Jackson. If all goes as scheduled, Jackson's first start will come April 11 at Texas.
Jackson, who does not have any remaining options -- which may have played a factor in the team's decision -- found himself on the other side of the coin this spring from when he was cut in the spring of 2006 after pitching well.
"It's definitely a different feeling being on the upper end of it," Jackson said.
The Rays' starting rotation is now set as follows: Kazmir, Jae Seo, James Shields, Casey Fossum and Jackson.
"This is a group of competitors," Jackson said. "We're going to go out and challenge hitters."
The final decision came down to Jackson or Howell. Rays manager Joe Maddon described the decision as a very hard one.
"That's about as close [a competition] as you can get," Maddon said.
Howell was optioned to Triple-A Durham Wednesday morning and said losing the competition hurt.
"I did everything I said I was going to do and worked hard," Howell said.
Howell posted a 1-1 mark with a 1.80 ERA in six spring appearances. The Rays want him to go to Triple-A Durham and start rather than work out of the bullpen in the Majors.
Other cuts: The Rays pared the roster down to 34 when Corcoran was optioned to Durham and right-hander Scott Dohmann was outrighted to Durham.
Corcoran pitched in the Rays' starting rotation in 2006 and was a popular player in the clubhouse.
"Things as they are, a move has to be made," a visibly disappointed Corcoran said. "[There was] a lot of competition this spring -- a lot of young competition, and everybody's pitching well. You can't dispute that. A decision was made. You don't have to like it, but you live with it."
Corcoran went 1-1 with a 5.73 ERA in six appearances.
"I'm a little bit upset," Corcoran said. "But time goes on and you get over it."
Final tune-up: Kazmir made his final start of the spring Wednesday against the Phillies. The Rays' Opening Day starter allowed one run on five hits and two walks in three innings, with four strikeouts and a wild pitch.
"I just felt good, [with] all of my pitches," Kazmir said.
Kazmir, who pitched little in the second half of the 2006 due to a sore shoulder, said spring exceeded his expectations.
"[It was] actually even better," Kazmir said. "[I was pleased with] how my arm feels and how my body feels."
This and that: Maddon expects that Rocco Baldelli (right hamstring) and Dioner Navarro (left hamstring) will be healthy enough to play by Opening Day. Both players played for Durham on Wednesday. Baldelli only hit and went 2-for-4 with a double, a single and a run scored. Navarro caught four innings and went 1-for-3. ... Catcher Josh Paul (bruised right hand) caught five innings for Double-A Montgomery on Wednesday and went 0-for-3. ... First-base coach George Hendrick remains on the shelf after having knee surgery Friday in St. Petersburg. Hendrick is expected to be out a week to 10 days, which could leave the first-base coaching duties to special advisor Dave Martinez or bullpen coach Bobby Ramos.
Up next: The Rays will travel to Fort Myers on Thursday afternoon to play the Red Sox at 1:05 ET. Jackson will start for the Rays in his first start since being named the team's No. 5 starter. Clay Buchholz will start for Boston.