By the time Masterson's day was done, he had allowed just two hits and one run over six innings, with his only real blip coming on a hanging breaking ball hit for a home run by Mike Napoli leading off the fifth.
"Gosh, that was really impressive," Red Sox catcher Kevin Cash said. "[He was] definitely the bright spot of the day. Anybody is going to have nerves in that situation. He was so composed. He was drastically, offspeed-wise, improved from even Spring Training. And we used it a lot and were able to keep him off-balance."
Masterson didn't allow a hit until Gary Matthews Jr. singled to center in the third.
"It was actually pretty good," Masterson said of taking the mound for the first time as a big leaguer. "When I first got out there, it felt nice. Then we got through the first inning and I had to remember I had to go out and do it again. That's when the nervousness got there. It was just fun. I was happy to have the opportunity."
Masterson found out about his opportunity less than 24 hours earlier at his Portland, Maine, home.
"Last night, I was at home with my wife trying to figure out something to do and my coach, Mike Cather, called and said, 'Are you ready for your start?'" Masterson said. "I said, 'Yeah.' He said, 'Good, because it's going to be at Fenway,'" Masterson recalled. "Then I scrambled to get everything together and drove down here."
The reason why Masterson was called up from the Portland Sea Dogs was the rapidly moving flu bug running through the Sox's pitching staff, affecting no fewer than four pitchers.
"I really just put the team in an opportunity to win," Masterson said. "That's what the starting pitcher's role is."
He allowed just two hits and one run with four walks and four strikeouts as the Red Sox had a 3-1 lead entering the seventh.
"Coming up, I was hoping to help out," Masterson said. "There are some unfortunate things that happened, and we didn't get the victory today, but I just wanted to go in and throw a lot of strikes. I did walk four people, but other than those four walks, I thought I pounded the zone pretty good and was happy with that."
And Masterson will have to be happy with that for the time being, as he was optioned back to Portland following the game to make room for reliever Bryan Corey, who will have his contract purchased from Triple-A Pawtucket prior to Friday's game against the Rays.
Even those in the opposing dugout couldn't help but take notice and be impressed.
"He handled himself real well out there," Angels manager Mike Scioscia said. "He's got a good arm. As the day went on, we had some better at-bats against him."
Sensing that his day was over after 95 pitches, the sellout crowd of 37,848 rose to their feet for a standing ovation.
Francona summed up the feelings of the appreciative fans and everyone in a Red Sox uniform alike.
"He did a great job," Francona said. "As an organization, I don't think we could be prouder."