As the player to be named later -- with emphasis, in his case, on later -- Gregerson arrived in Peoria late and with little time to make a good impression.
Even Gregerson didn't give him much of a shot to make the 25-man Opening Day roster.
"I thought every second of the day that I was heading to Triple-A," said Gregerson, who was part of the deal that sent Khalil Greene to St. Louis on Dec. 4, 2008. " ... I had no thought at all that I would be on the team, mostly because I came late, the pitchers we had here already. It got to be pretty stressful at the end."
Finally, on the day before the regular season started, Gregerson, the right-handed reliever, sat in front of his locker at PETCO Park, waiting for the call. Finally, manager Bud Black let him know he was on the team.
"We had some good reports on him," Black said. "For us, it wasn't a huge leap of faith. What we saw, we liked. He got his opportunity and made the most of it.
"At that point [in Spring Training], we realized that our bullpen was unsettled. We didn't know what direction we were going to go. It had to get us thinking about making some changes."
Gregerson took care of the rest.
The 25-year-old went 2-4 with a 3.24 ERA in 72 games last season and limited opponents to a .221 batting average. Better still, aside from being durable and a dependable factor in the bullpen, Gregerson was nearly unhittable at PETCO Park.
Gregerson had a 0.65 ERA at home, allowing 19 hits in 41 2/3 innings with 53 strikeouts and opposing batters hit .136 against him.
He ranked fourth in the National League in strikeouts per innings pitched (11.16), trailing only Jonathan Broxton (13.50), Rafael Soriano (12.13) and Carlos Marmol (11.31).
Aside from a rocky April (4.72 ERA), Gregerson proved he was someone Black could lean on in the seventh inning of games and be a bridge to eighth-inning specialist Mike Adams and then closer Heath Bell.
Not bad work for someone who hadn't pitched the Double-A level before 2009.
"I got the nerves out of the way fairly quick," Gregerson said. "When I went out there, I threw to my strength as a pitcher. Once I saw I could get guys out, it gave me more and more confidence."
That strength, primarily, as a slider that former general manager Kevin Towers liked to refer to as a "wipeout slider," a pitch with such dramatic late movement that hitters had trouble squaring up on the bat.
Gregerson actually threw his slider (49.3 percent) more than his fastball (45.3), which is something he would like to change this season. The slider is still his No. 1 pitch, but like other pitchers in camp and at the heeding of management, fastball command is being urged strongly.
The Padres like the natural sink Gregerson gets on his pitches, which certainly helped him last season as he got 45.7 of his outs on ground balls.
"My slider is there and I've been throwing it in camp. But I'm not throwing it as much," Gregerson said. "I'm really working on my fastball command, throwing it away to the right-handed hitters and working on my sinker command. Once I can do that, I'm going to be able to do some good things."
Either way, Gregerson knows he's in a much better place now with the Padres than he was with the Cardinals. Actually, he realized as much that day last March when he was throwing on a back field, under the watch of Padres management.
"It was weird for me," Gregerson said of the trade. "But I personally felt like the interest in me went up dramatically going from St. Louis to San Diego. You had all those guys watching you. There was a little more added pressure initially. But it was good for me, though."
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.