Rivera, 23, was ranked as Houston’s No. 14 prospect, according to MLB Pipeline, and he has thrown as hard as 101 mph. The Angels must keep Rivera on the 26-man roster for the entire 2021 season, or else he must be offered back to the Astros for $50,000.
"He has a quality arm, big fastball anywhere from 95 to 98, with a pretty good profile from a movement standpoint," Angels general manager Perry Minasian said. "He performed well in 2019, especially the last 15 appearances. He really took off. He has the makings of a quality breaking ball and has a quality change. He hasn't experienced the upper levels, but we felt like with this type of talent, we wanted to at least take a look at it and give it a shot."
Rivera went 5-5 with a 3.81 ERA, 95 strikeouts and 36 walks in 75 2/3 innings with Class A Quad Cities in 2019. He made 11 starts and seven relief appearances while serving in a hybrid role. The Angels are likely to use him in relief this season but aren't ruling him out as a starter in the future.
"I wouldn't close the door on anything," Minasian said. "From a big league standpoint, any role is difficult. But he's done different things in the past, so I wouldn't necessarily want to box him into a certain role. We'll take a look at what we have and come up with a plan and go from there."
Rivera is still developing his secondary pitches, but his changeup has improved and he also possesses a power slider. He was signed for $10,000 out of the Dominican Republic in October 2016 as a 19-year-old.
Soriano, meanwhile, was ranked as the Angels’ No. 13 prospect by MLB Pipeline. He underwent Tommy John surgery in February, which kept him out of action in 2020. Like Rivera, he has plus-velocity and has hit triple digits on the radar gun. He posted a 2.51 ERA across Rookie level and Class A in '19, with 92 strikeouts and 51 walks in 82 1/3 innings.
"It's always a tough decision," Minasian said. "There's only a certain amount of roster spots. He's a great kid and we're excited for him to get that opportunity, but at the end of the day, decisions have to be made and we feel good with the player we took."