But then he settled in and sat down the next 10 batters to put himself well on his way to his first Double-A victory.
The right-hander allowed two runs on just one hit and four walks, fanning five, over six innings as Reading topped Binghamton, 5-2. It was the second start Colvin made for the Phillies since being called up from Class A Advanced Clearwater at the end of July.
"It definitely feels good," said the 21-year-old. "I had fastball command, kept it down, got some quick outs, the defense is always good behind me."
Colvin, the Phillies' No. 3 prospect, was 5-6 with the Threshers, posting a 4.27 ERA in 23 Florida State League appearances over 105 1/3 innings. He'd struck out 93 and walked 51 before his promotion to the Eastern League, where he said he was happy to be finishing his season.
"I actually heard from the pitching coordinator [about the callup]," Colvin said. "I like everybody, I've played with a lot of these guys earlier in my career, so I'm happy to be back with them."
Colvin made his Double-A debut for Reading on July 31 at Richmond. He surrendered three runs on nine hits without walking a batter over five innings, but didn't factor in the decision in an eventual 6-4 win for the Phillies.
Sunday was his first start, though, at his new home ballpark, FirstEnergy Stadium, and he seemed to take to the new surroundings.
"I think I'm making the transition pretty smoothly," he said. "Go out there and keep throwing strikes, keeping getting wins, that's what I'm hoping."
MLB.com's No. 66 overall prospect said one of the starkest differences in the jump from Class A Advanced to Double-A was the higher demand for control, with strike zones appearing a little smaller and hitters more selective.
He also said he hoped that he wanted to begin his outings a bit more smoothly.
"The zones are tighter, hitters aren't swinging at missed pitches, so you definitely have to be throwing strikes," Colvin noted. "You want to cut down on the walks, you never want to walk anybody, so you're always trying to keep those down.
"And I've been giving up runs in the first inning. I want to come out in the beginning better."
Colvin is 1-0 with a 4.09 ERA in his two starts for Reading, with six strikeouts and four walks in 11 innings. He had thrown 222 innings in the Florida State League between last year and this year before finally getting his promotion to the Eastern League.
"I was really happy to get out of the Florida State League, definitely happy to be here with these guys," he said.
On Sunday, Cody Asche hit a three-run homer and Darin Ruf went yard for the 22nd time this season to lead the Reading offense.