If anything, the decision has grown tougher and more multi-faceted as camp has progressed. Jason Berken and David Hernandez have both turned in solid performances as of late, furthering speculation that Tillman -- who labored through 4 1/3 innings Friday -- could start the season at Triple-A.
"The thing we try to impress on the kids is the obvious fact that nobody uses the same 12 pitchers all year," MacPhail said. "The beginning of the season is just a snapshot in time."
MacPhail said that Hernandez and Berken are "absolutely" still in contention for the team's fifth spot, and he acknowledged that the heated competition has been a welcome one.
"What I was telling our staff is we got guys competing for our spots and we don't have spots competing for guys," MacPhail said. "And that is a pleasant development, particularly as it relates to our pitching."
Trembley has called the team's bullpen competition a dogfight, and following Hernandez's five shutout innings of Saturday's 6-1 win over the Red Sox, he used a similar comparison to describe what's going on with the back end of the rotation.
"I would say we're going to go 15 rounds with it," Trembley said. "We're going to go the distance and keep battling and keep running these guys out here and try to make the right decision and the best decision. Guys are answering the bell, and they're making it real tough for me. And I like it."
The Orioles will go with a 12-man pitching staff this season, which places a premium on having flexibility in the bullpen, which guys such as Berken could potentially provide. A scenario such as April 8 and 9 -- where the team will play a night contest vs. the Rays in St. Petersburg, Fla., before its home opener at 3 p.m. ET in Baltimore the next afternoon -- puts extra emphasis on having pitchers who can toss multiple innings of relief.
Baltimore plays 16 consecutive games starting April 6 vs. Tampa Bay, which leaves no opportunity to skip a rotation slot. It also puts the O's bullpen in a tough spot should a starter falter and force an early exit.
Hernandez has thrust his name to the fifth-starter forefront with his recent outings. He retired nine of the first 10 Red Sox batters he faced Saturday, allowing four hits over five scoreless innings with six strikeouts. He lowered his spring ERA to a 3.00 in the process, and impressed Trembley with his tenacity and ability to escape several key jams -- including a bases-loaded, no-out scenario in the fourth.
"You want to see if somebody's going to cave in or not," Trembley said. "You probably get a much better read from your players when things aren't going according to plan. You've got to see what people can do through a little bit of adversity, because they're certainly going to be tested in the regular season."
Although he started the spring pitching out of the 'pen, Hernandez has capitalized on the recent opportunities he's been given to start. He made his first appearance as a starter on March 16, and is 1-1 in two official Grapefruit League starts, which doesn't include a 75-pitch outing in a Minor League game last week. In 15 innings, Hernandez has allowed five earned runs, and he has 20 strikeouts to three walks. Hernandez said Saturday he has not been given any indication as to where -- or in what role -- he will start the season.
"I'm just trying to go out there and do the best I can every performance," Hernandez said. "Whether it's good enough or not, all I can say is I went out and gave it my best effort. And [Saturday], the results indicated that."
To his credit, Tillman has said all along that he has approached this spring as a situation he must win, rather than have it handed to him. The 21-year-old was visibly frustrated with Friday's performance, which was an 88-pitch outing that yielded two runs on four walks and four hits. It's worth noting that Tillman's struggles came against a Minnesota lineup that didn't have the power bats of Justin Morneau and Joe Mauer, two Twins who would certainly be in a regular-season game.
In five spring games, Tillman has a 3.86 ERA, allowing seven earned runs over 16 1/3 innings. His strikeout-to-walk ratio (9K/10BB) is a glaring statistic, particularly given the fact that the Orioles have made it clear the kid gloves are off and they won't carry that extra 13th pitcher.
Although Berken is still considered more of a long shot to swoop in for the fifth spot, he has pitched his way into recognition, particularly in that sorely needed middle-relief role.
Following Tillman's early exit Friday, Berken tossed four scoreless innings, allowing two hits and collecting three strikeouts. So far, he has not been stretched out as far as the other two, but Berken has had a solid spring nonetheless. In six games, he's allowed four runs over 12 2/3 innings, three of which came in his only start on March 17. Berken has a 2.84 ERA this spring, with seven strikeouts against three walks.
While the decision will likely come down to the end of Spring Training, MacPhail acknowledged that the three would certainly benefit from knowing their roles to start the season.
"The sooner the people know where they are going to start the year, the better," MacPhail said. "The last time I talked to the staff, I don't think we've come to a resolution yet. Because you want to let these guys go out and get the opportunity to compete and give them a fair shot at it."
Brittany Ghiroli is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.