As it turns out, Mortensen was far more than roster filler.
If the Red Sox had been able to pull out a comeback victory, Mortensen would have been one of the prominent figures. Instead, he was a footnote in a 4-2 loss to the A's.
All Mortensen did was reel off three brilliant innings, allowing one hit and no walks while striking out six.
"When you haven't seen a guy, you're pulling for him, but you really don't know what to expect and you have to protect against something that might happen," manager Bobby Valentine said. "He was fantastic. His offspeed stuff in the bullpens in Spring Training looked terrific. Then in the games he seemed to elevate a little. Often we said if it's down, it's really tough. It was down tonight and it was really tough."
Mortensen replaced first baseman Lars Anderson, who was optioned back to Pawtucket after Tuesday's game, on the 25-man roster.
A right-hander who was starting at Pawtucket, Mortensen is the player the Red Sox acquired from the Rockies in exchange for Marco Scutaro back in January.
"He was scheduled to start Thursday, so he was the most rested arm that they had at Triple-A who is on our roster," said Valentine.
Mortensen, who has pitched in 23 Major League games, is excited for the opportunity in Boston.
"It's awesome. It's great to be up here. I'm excited, really excited," Mortensen said.
It remains to be seen how much longer Mortensen will be on the roster, but he showed Wednesday that the team might want to think twice before sending him back down.
"I'm just trying to do my thing," Mortensen said. "Hopefully I do stay and if not that's fine, keep working down there and get back up here."