The club also brought up lefty Arthur Rhodes, who missed all of last season after Tommy John elbow ligament replacement surgery. He had been working his way back at West Tenn.
Rhodes takes right fielder Mike Morse's spot on the roster. Morse dislocated his left shoulder diving for a ball in the sixth inning Sunday. He was placed on the 15-day disabled list.
The staff is now at 12 pitchers for the first time because of the recurring hip injury to starter Erik Bedard. He missed his scheduled start Sunday because of hip issues. Bedard will throw a bullpen session this week to determine how he feels and when he can be reinserted into the rotation.
If Bedard is still hampered, manager John McLaren said Dickey could fill that start on Friday against the Angels. In the meantime, Dickey will work out of the bullpen.
"We're not sure what role he's going to have," McLaren said. "We're still getting our feet on the ground until J.J. Putz (ribs) gets back, [Brandon] Morrow (shoulder) gets back and Bedard is healthy."
Dickey, 33, the first knuckleballer to reach the big leagues for the Mariners, has made two starts, compiling a 1-1 record and 2.40 ERA. He has struck out 11 and walked one. In his last start, Wednesday against Fresno, he carried a no-hitter into the seventh.
"It's not a pitch [knuckleball] you ever perfect. It's a pitch you kind of have a relationship with," Dickey said. "We're kind of a exclusive brotherhood. It's going to take a lot of patience, a lot of practice and a lot of mental stability on my part. It's been a rewarding journey to get here, but it's also been a little difficult."
Dickey was selected by Seattle from Minnesota in the Major League Rule 5 Draft on Dec. 6. On March 29, Seattle sent Minor League catcher Jair Fernandez to the Twins for the rights to keep Dickey.
Rhodes, 38, was 0-0 with a 1.93 ERA in five Spring Training games.
"Tommy John [surgery] is a long surgery, 2 1/2 hours, but the doctor said, 'You'll be able to pitch again,'" Rhodes said. "I decided to beat that [12- to 14-month deadline]. I worked hard the whole offseason. I wanted to be in the big leagues by mid to the end of April. That was my mind-set."
Rhodes has a career record of 75-60 with a 4.31 in 653 big league games (61 starts) with Baltimore (1991-99), Seattle (2000-03, 2007), Oakland (2004), Cleveland (2005) and Philadelphia (2006). He is 26-15 with a 3.07 ERA in 276 career appearances with the Mariners.
Morse was hitting .222 in five games with one double. He set a new Mariners record by hitting .492 this spring. Doctors examined him Monday night, and there's still the possibility of surgery since the labrum and rotator cuff could be involved.
O'Flaherty, 23, appeared in seven games, allowing runs in six of them. In 2007, O'Flaherty was first among Mariners relievers in wins (7), fourth in innings (52 1/3), fifth in appearances (56) and sixth in strikeouts (36), while holding left-handed hitters to a .183 batting average.
"We had to get Eric his confidence back," McLaren added. "He's been struggling so much."