Thatcher and Gregerson returned to Petco Park as visitors as their new team, the Astros, opened a three-game series against the Padres.
Even though they dressed in the visiting clubhouse, being back in San Diego felt a lot like home, they both said.
Thatcher played parts of seven seasons (2007-13) with the Padres, a lefty-on-lefty specialist who was traded to the D-backs in July 2013.
Gregerson, the closer for the Astros, played five seasons for the Padres (2009-13) before being traded to the A's in the winter of 2013.
Together, they've been reunited in Houston. Before that, though, the two became fast friends in the Padres' bullpen.
"The Padres are the ones who gave me the opportunity to play at this level … and playing with Joe, we sat side-by-side for five years," Gregerson said. "I've been to his wedding. He's been to mine. Having him here now is awesome for me."
Thatcher and Gregerson said that Padres manager Bud Black and pitching coach Darren Balsley deserve a lot of credit for where they are now.
"I'm really grateful to Buddy and Balsley," Thatcher said. "They gave me a lot of chances to succeed. The early part of my career was a little rocky, but they had faith in me and believed in me. They put a lot of trust in me."
Gregerson was acquired by the Padres from the Cardinals late in Spring Training for 2009, completing the deal between the teams that had sent Khalil Greene to St. Louis. He hadn't pitched above Double-A but flourished with the Padres.
Gregerson had a 2.88 ERA in 363 games pitching late in games for the Padres. He helped set up closers Heath Bell and Huston Street.
"As a young kid coming up, they gave me an opportunity, gave me every chance to succeed," Gregerson said. "And even those days when I wasn't pitching so great, they had no problem throwing me out there the next day.
"That was helpful for a young player to go out there. It helped me become a more confident player."