The 24-year-old from Sammamish, Wash., worked through three scoreless innings and had a 2-0 lead going into the fourth, but he wound up taking the loss as he allowed eight hits and four runs in 4 2/3 innings.
Manager Scott Servais said Sampson understandably wasn't as sharp as he's been in his Minor League outings, where he put up a 7-4 record and 3.25 ERA in 13 starts at Triple-A Tacoma.
"He was getting the first one under his belt," Servais said. "I look forward to his next one and I think he'll be much more under control. There were probably more pitches up today than what you normally see out of him. He works at the bottom of the strike zone and then elevates late. It took him a while. That is going to happen. It's very normal."
Sampson gave up home runs to Jackie Bradley Jr. and Xander Bogaerts, but he's not the first to get roughed up a bit by the American League's highest-scoring team.
"My thing is hitting spots, being down in the zone and having good sink on my ball," Sampson said. "I think early I was a little jumpy and had a lot of adrenaline going and the ball was up, my slider was a little flat and my changeup wasn't as good as I want it to be. But overall, my stuff was decent. It wasn't what I needed to get these big league hitters out, but I think next time it'll be a lot better."
Sampson said he met briefly with the 19 family and friends who flew out for the game, then took in the Fenway scene while warming up in the outfield before locking in on the task at hand. But yeah, it's hard not to be a little awestruck when facing the likes of David Ortiz, who went 1-for-2 with a single against him.
"You see him in there and you've seen him on TV all the time," said Sampson. "But you kind of lose sight of it. I was more focused on [catcher Steve] Clevenger back there. But for how much he's done in his career, it's pretty special."
Sampson's own career is just beginning. Having grown up in the Seattle area -- pitching for Skyline High School in Sammamish and Bellevue College before being drafted by the Pirates in the fifth round of the 2012 Draft -- he became just the sixth Washington-born pitcher to make a start for the Mariners. Sampson was acquired from the Pirates last July 31 in a Trade Deadline deal for veteran lefty J.A. Happ.
Sampson figures to get at least one more outing Thursday in Detroit before Miley's earliest possible return on June 28. But this one will always be his first, and he will learn from it.
"It's the same game," Sampson said. "Like [catcher Chris] Iannetta was telling me, it's the same glove. I've been using the same glove the whole time. After the first guy, everybody has holes in their swings and you just have to make adjustments. But it was awesome."