PHILADELPHIA -- Despite a strong Spring Training, right-handed reliever Tanner Rainey was left off the Reds' 2018 Opening Day roster. He didn't have to wait long for a welcomed conversation, though.
The Reds selected the contract of Rainey from Triple-A Louisville and designated right-hander Yovani Gallardo for assignment on Tuesday. Rainey made his Major League debut during Tuesday's 6-1 loss to the Phillies, working one inning, allowing four earned runs on two hits, one of which was a grand slam off the bat of Scott Kingery. In the outing, he recorded his first two big league strikeouts. 
"It didn't really cross my mind," Rainey said about the possibility of being called up before he got the news. "It was indescribable. There are no words for that feeling."
The No. 29-ranked Reds prospect according to MLB Pipeline, Rainey has made two hitless relief appearances for Louisville this year, striking out five and walking one in two innings. He posted a 3.19 ERA in 62 innings in the Minors last season.
Rainey impressed the Reds throughout the spring. The 25-year-old had a 2.16 ERA, a .167 batting average against and 13 strikeouts in 8 1/3 innings during seven Spring Training appearances.
"That was my idea coming into spring," Rainey said. "I didn't necessarily try to do too much, but I wanted to show them what I could do and give them a reason to get me here."
Rainey, who was not on the Reds' 40-man roster, received word of the promotion on Monday night. He was on a flight from Louisville to Philadelphia early on Tuesday morning and was available to pitch against the Phillies on Tuesday night.
"It's a big arm. It's a 95- to 98-mile per hour fastball with a hard slider and a changeup," Reds manager Bryan Price said. "He's a pretty polished guy. We're going to get him acclimated to the bullpen and get him in there."
Gallardo, 32, was signed as a free agent on March 30 and made three relief appearances for the Reds, allowing eight earned runs in 2 1/3 innings. He is 113-93 with a 3.97 ERA in 301 appearances (289 starts) over 12 big league seasons, eight of them with the Brewers. He was a National League All-Star in 2010, when he went 14-7 for Milwaukee.
When a player's contract is designated for assignment -- often abbreviated "DFA" -- that player is immediately removed from his club's 40-man roster, and 25-man roster if he was on that as well. Within seven days of the transaction (it was previously 10 days), the player must either be traded, released or placed on irrevocable outright waivers.