Matos was optioned to Triple-A Fresno and Romo was designated for assignment. The club couldn't option Romo directly to Fresno because he'd been put on revocable trade waivers, but he's expected to join the Grizzlies on Friday at Salt Lake.
In corresponding moves, relievers Keiichi Yabu and Billy Sadler returned to the active roster. Yabu was activated from the disabled list after fully rehabbing a sprained right finger. Sadler, meanwhile, joined the club after more than a month with Fresno.
Before being optioned in early July, Sadler had a 4.94 ERA in 24 relief appearances. In his past five outings with the Grizzlies, he tossed seven innings, allowing seven hits and two runs.
"He's done what we were hoping he'd do," said manager Bruce Bochy, who noted Sadler's improved fielding ability.
Yabu went on the DL on July 20 following a string of ineffective appearances in which he gave up four runs in 3 1/3 innings. But he said his finger is OK, and Bochy liked what he saw in Yabu's side session on Monday.
Both Yabu and Sadler will pitch in middle relief, with Yabu likely getting more frequent work. Bochy said Matos and Romo were sent down to pitch in a more "structured" environment, while Geno Espineli, originally called up to replace Yabu, stayed with the team because he's "resilient" and he's "a guy we could use anywhere."
Sending lefty Alex Hinshaw to the Minors wasn't an option. In the nearly three months he's been in the big leagues, Hinshaw's maintained a 2.51 ERA in 32 appearances.
"With the way he's thrown" Bochy said, "he probably has separated himself."
Both Matos and Romo were in street clothes before Wednesday's game started. Each seemed to take the news well, despite the fact they'd been mostly successful in their short Major League stints. Excluding their bad outings Tuesday, Romo (15 outings, 2.35 ERA) and Matos (12 outings, 2.13 ERA) had shown good stuff.
"I might have caught their attention a little bit," Romo said.
Bochy agreed, saying, "There'd be no hesitation on our part to bring them back [in the future]."
After spending nearly four years in the Minors, Hinshaw felt sympathy for his fellow relievers.
"I just told [Romo] to use it as motivation," Hinshaw said. "But yeah, it stinks, getting a taste of this and then having to go back to the Minors."
David Biderman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.