"I was surprised, I wasn't really expecting it," he said.
Hampson, who was 4-3 with a 2.33 ERA in 51 appearances in Buffalo, quickly changed plans. He jumped on the first plane to St. Louis and was activated in time for Tuesday's contest.
Meanwhile his wife, Wendy, and the couple's two girls were given the chore of driving back with the family belongings.
Hampson made his long-awaited St. Louis debut on Tuesday night, giving up one run in one inning in the Mets' 5-1 loss to the Cardinals. He surrendered a lead off single to Daniel Descalso in the sixth. Descalso eventually came around to score on a one-out groundout by Jon Jay.
"It was really nice -- I got out on the mound, looked around and took a breath," Hampson said. "I definitely enjoyed the moment."
Hampson would have loved a clean 1-2-3 inning, but he was pleased with the effort.
"It was cool to get out there in the place where I came to games," he said.
Wendy and the children were still in Buffalo tying up some loose ends. But his parents and about 20 other friends and family were in the stands to see Hampson in action.
"I heard them yelling when I came out of the bullpen," Hampson said. "I was hoping they would take it easy."
Hampson did not allow a run in three relief appearances with the Mets earlier this season. The Bisons ended their season on Sunday.
Hampson made his big league debut with the Colorado Rockies on Sept. 10, 2006. He pitched in 74 games with San Diego in 2007-08 and underwent shoulder surgery in '09.
The Mets signed him to a Minor League contract on Feb. 16, 2011.
After a strong start in Buffalo, the Mets called him up on June 25, but he was sent back down 11 days later.
Mets manager Terry Collins and general manager Sandy Alderson have been keeping a watchful eye on Hampson.
"He's a strike-thrower," Collins said. "He's not an overpowering guy, but he knows how to use his pitches."
Hampson, who attended nearby Edwardsville High, had a pass list of about 25 for the games Tuesday and Wednesday.