"'Cause I quit working out," said Helton, who has yet to make a retirement announcement. "I haven't worked out since the All-Star Game. I just let it go."
After years of back issues and coming off a 2012 that was shortened by season-ending surgery to repair a torn labrum in his right hip, Helton is healthy. He's also taking an unburdened mental approach.
"I'm just swinging hard, hoping for a sound, and every once in a while, I'm hearing it," he said.
The homer was his 10th at Petco Park, which ties him with Pablo Sandoval, Justin Upton and Adam LaRoche for the most there by a visiting player. Helton has a .344 batting average and .453 on-base percentage at Petco, which opened in 2004.
The long ball was also the 31st ninth-inning homer of his career. Among active players, only Alex Rodriguez (40) and Jason Giambi (33) have more.
Manager Walt Weiss, who was a veteran shortstop with the Rockies when Helton debuted in 1997, is marveling at Helton's strong finish.
"He's putting some good swings on the ball, hitting it in the gaps and over the fence," Weiss said. "It's been fun to watch.
"We've tried to be smart about how we run him out there, but we've actually run him out there pretty regularly this year. He hasn't had the back issues and some of the nagging injuries he's had the last few years. As long as he's healthy, I always felt he'd be a productive player this year."
Thomas Harding is a reporter for MLB.com. Read his blog, Hardball in the Rockies, and follow him on Twitter @harding_at_mlb. This story was not subject to the approval of Major League Baseball or its clubs.