Gaviglio will make his Royals debut Thursday after officially being named Kansas City's starting pitcher for the opener of its four-game set against the division rival Minnesota Twins.
Gaviglio, 27, was 3-5 with a 4.62 ERA in 12 games (11 starts) with the Mariners this season. He also recorded a 3.88 ERA in 13 starts for Triple-A Tacoma.
"Each start was a learning experience," Gaviglio said. "Towards the end, I got a little mechanically off, but I feel like I got back to my normal mechanics. I'm excited."
Yost said Gaviglio is capable of throwing 90-95 pitches Thursday.
"They were on a program over there where they were going 80 pitches and getting their starters out," Yost said. "So, yeah, he's stretched out."
The announcement capped a whirlwind week for Gaviglio, who was claimed off outright waivers from Seattle last Friday.
Gaviglio first became aware of the news on a runaway in Las Vegas after traveling with his former team from Tacoma -- mere hours after tossing four innings of one-run ball.
"I had just got off the flight to Vegas, and my phone started exploding," Gaviglio said. "I was trying to put it all together, so, yeah, it's been exciting."
Gaviglio parted ways with his former teammates, and hung around in the airport before catching a flight to Minnesota to join the Royals.
"I was fortunate enough -- I lived with my aunt in Tacoma," Gaviglio said. "So, I don't have to worry about my stuff going anywhere, or getting out of my apartment. That makes it nice."
A former fifth-round Draft pick of the St. Louis Cardinals in 2011, Gaviglio was traded to Seattle in exchange for utility man Ty Kelly following the 2014 season.
Gaviglio will fill the spot in the rotation vacated by Royals starter Danny Duffy, who is recovering from a muscle strain near his left elbow.
"I'm really excited," Gaviglio said. "I'm looking forward to helping this team out."
• Joakim Soria and Duffy each threw 17 pitches off the mound Wednesday. Barring a setback, both pitchers are scheduled to throw a second session -- roughly 15-25 pitches -- Friday in Kansas City. There's no timetable for their return, but both pitchers are expected to rejoin the team later this month.
"Chances are, you'll get [Soria] back sooner, because he's a reliever. He only needs to pitch one inning or so," Royals pitching coach Dave Eiland said. "Danny, being a starter, has to pitch a bunch more than that. But it's their first time on the mound in a while, so you withhold judgment until you see how they come out of this."