The right-hander retired Jay Bruce, Devin Mesoraco and Skip Schumaker with three groundouts.
"Felt amazing, I can tell you that," Jeffress said after his return to the Miller Park mound. "[There were] nerves a little bit, but to be honest, I felt very comfortable. Once I got that first pitch out of the way, it was great."
Jeffress, Milwaukee's 2006 first-round Draft pick who was traded to Kansas City in the Zack Greinke deal, re-signed with the Brewers earlier this season. He was promoted from Triple-A Nashville on Monday to boost a struggling bullpen. The righty was able to showcase his power arm immediately with Nashville, and his new manager took notice.
"That's some nice stuff there," Brewers skipper Ron Roenicke said. "Power arm. It's got movement on it. Strikes. You couldn't impress more than he did in that inning.
"Everything was down low. Got a couple breaking balls up, one he threw down nice. It looks like an easy delivery, and man, that ball comes out and it's not straight. It's got movement on it."
The Brewers have depended on lefties Will Smith and Zach Duke in high-leverage situations but have struggled to find a right-handed power arm to complement closer Francisco Rodriguez. Roenicke suggested that he may start putting Jeffress into closer games if the matchups and situation dictate it.
Jeffress can certainly be pleased with the early impression he left on his teammates in his first Brewers appearance since 2010.
"Man, that's a breath of fresh air right there," said Mark Reynolds, who hit a pair of home runs. "He's always had the stuff, but to come in and throw strikes, that's huge for him. I'm sure he felt good being back out there. To see a guy throwing 98, 100 mph late in the game is welcomed by any team. Hopefully, he figured it out down in the Minor Leagues, and he can be a big addition to our club."
Adam McCalvy is a reporter for MLB.com. Read his blog, Brew Beat, and follow him on Twitter at @AdamMcCalvy. Caitlin Swieca is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.