Riefenhauser retired the first batter he faced, Alfonso Soriano, on a groundout. He then worked the eighth, retiring the Yankees in order to end his outing.
"I couldn't be more happy," Riefenhauser said. "[Joel] Peralta gave me a head's up. He said, 'Hey, man, just go out there and throw strikes.' And that's what I tried to do.
"This is probably the most jacked up I've ever been, even if it [had been] a 3-2 game in the ninth. This was a different ballgame. This was a lot of fun."
Maddon complimented Riefenhauer's performance.
"Kind of stone-faced, I loved it," Maddon said. "He threw [two] balls and 10 strikes. Totally composed. Outstanding first performance, does not surprise me in the least."
Maddon noted that Riefenhauser can retire right-handers as well as left-handers, "but he's really good against lefties."
"He's got a nice breaking ball/slider for his other pitch," Maddon added. "He throws the ball pretty hard, and he's not afraid. So he's got a nice combination of things."
Riefenhauser was a 20th-round selection by the Rays in the 2010 First-Year Player Draft.
"I talked to him a lot [during Spring Training]," Maddon said. "He's just a really nice kid, really unpretentious. I think he's grateful for being here, but he's also earned the right to be here. So that's pretty cool when you get a guy like that, drafted in the low rounds and works his way up through the ranks. And every year you just keep hearing his name, 'Riefenhauser, Riefenhauser.' And I finally got to see him this past Spring Training and got to see what all the talk was about. He's good. He's good. He's really good on lefties, but he's going to get out righties, too."
Riefenhauser sounded appreciative of the treatment accorded him by the Rays.
"[The organization] always sees something in you, and they try to bring it out," said Riefenhauser, a native of Mahopac, N.Y., which is about an hour away from Yankee Stadium. "And I couldn't be more blessed to have this opportunity here, especially against the team I grew up loving, and it's really something."
Meanwhile, Boxberger returned to Durham with an unblemished slate, including a standout two innings of scoreless relief in Friday night's win over the Yankees.
Maddon was clearly impressed with Boxberger, who allowed no runs on one hit and two walks while striking out four in four innings over three appearances.
"Boxy is a Major League pitcher, period," Maddon said. "Sometimes the rules work against you on pitchers and young players, but there's going to be a time when it's going to work in his favor also. He's a professional. I emphasized to him ... how much confidence I have in him against anybody at any time. He's got that kind of stuff. He can pitch against righties and lefties at big moments."