"For me, you look at what Jarred Cosart was able to do last year, I was pretty comfortable with him being one of the guys who was going to be in our rotation," Porter said. "Last night, you got a chance to see a guy who has an opportunity to be a front-of-the-rotation guy. When he's locked and if we get that type of consistency, he's going to pitch to his potential."
Cosart, who grew up in Houston, said he's a huge fan of Derek Jeter, the Yankees shortstop who will be making his final appearance in Houston during the series against the Astros. Cosart said to be in the rotation to start the year is an honor.
"My future goal is to be a No. 1 one day," he said. "There's no one more deserving this year than Scott. He's helped us young guys out a lot. Now we're kind of going with the mindset we're trying to [start off on] the right foot, and that would be to win a series. That's our goal."
Oberholtzer was impressive as a starter as a rookie in 2013, going 4-5 with a 2.24 ERA in 10 starts.
"It's a great opportunity, for one," he said. "But it's also an honor to be named as one of the five to break as Opening Day starters. It's something I had in mind to make an Opening Day roster since I was young. It's a dream come true, and hopefully I can continue the success I had last year for many years to come."
Porter said right-handers Lucas Harrell, Jerome Williams and Brad Peacock and left-hander Dallas Keuchel are the remaining candidates for the final two spots in the rotation.
"As we work through the competition for those final spots, all the guys taking the ball this next turn through, they all realize what's at stake," Porter said.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.