Hernandez -- who will make his Twins debut, but has one big league appearance with the White Sox under his belt -- said he found out from Triple-A Rochester manager Gene Glynn on Friday that he would start for Minnesota.
"I was in shock when Gene told me that I was going to the big leagues and going to start on Sunday," Hernandez said. "I said, 'What, are you kidding?' And he said, 'No,' and, 'Congratulations.' So I thanked him. It's exciting. I'm here and I'm ready."
Hernandez, who was acquired along with infielder Eduardo Escobar in the trade that sent Francisco Liriano to the White Sox before last year's Trade Deadline, will be making his second career start. He made a spot start for Chicago against the Red Sox last year and gave up eight runs in four innings.
But he fared better in the Minor Leagues with a combined 3.32 ERA between Double-A and Triple-A in two organizations last season, and excelled this spring with 11 scoreless Grapefruit League innings.
"It's going to be entertaining," Twins manager Ron Gardenhire said. "He had a good spring. We used him out of the 'pen. I think he made only one start, but he mostly came out of the bullpen. But he's a starter and has a good changeup and has a good fastball he can cut and a nice looping curveball."
Hernandez was scheduled to start for Rochester on Sunday, and Gardenhire said the lefty will likely throw about 75-85 pitches.
Hernandez said his wife, Jackie, and his daughter, Bianca -- born the same day he was traded to the Twins -- will be in attendance to watch him start. He said his goal is to impress Twins management and stick in the rotation, but that could be tough, as left-hander Scott Diamond is on track to return to the rotation Friday against the Mets.
"I'm going to try my best," Hernandez said. "And try to stay here all year."
Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger This story was not subject to the approval of Major League Baseball or its clubs.