Barfield hit a three-run homer with one out in the ninth inning to lift the Padres to a 7-5 win over the Colorado Rockies on Monday night.
The defending NL West champion Padres kept their 1½-game lead over Philadelphia in the wild-card race and pulled within two games of Los Angeles in the division.
Barfield, the son of former AL home run champ Jesse Barfield, homered on a 1-2 pitch from All-Star closer Brian Fuentes, his 12th homer of the season and first walkoff shot at any level.
"It's nice to get my first one -- Little League, high school, anything," Barfield said. "You try and do it all the time and it just never happens.
"Tonight I'm going to call my dad and give him a hard time. I think I've got one more walkoff to go to catch him."
Barfield finished with four RBI, atoning for an error that helped the Rockies take the lead in the fifth.
With the Rockies two outs from beating the Padres for the 11th time in 17th games this year, San Diego rallied against Fuentes (3-4).
"Anytime you walk two batters in the ninth inning of a one-run ballgame you're in trouble," Colorado manager Clint Hurdle said. "It's a tough situation to get out of. He's gotten out of it before. He didn't get out of it tonight."
Barfield fell behind 0-2 on nasty changeups before homering on a 1-2 fastball.
"He's real tough, so if you go up there looking to hit a home run or something like that, it's not going to happen," Barfield said.
It was Fuentes' fifth blown save in 28 chances. Rudy Seanez (1-0) pitched one inning for the win.
"It's frustrating that I didn't get the job done," said Fuentes, who allowed a run for the second time in 18 games.
"I just couldn't find it," he said of the walks. "I just didn't make quality pitches."
Fuentes hadn't pitched in a save situation since Aug. 9 at Los Angeles. His previous eight appearances were in non-save situations.
Williams walked Jamey Carroll leading off the game and Helton followed with his 14th homer.
San Diego went ahead 3-2 in the third, highlighted by Brian Giles' 12th homer. Barfield hit an RBI double, and another run scored when Dave Roberts hit into a double play.
Tulowitzki tied it with his 429-foot shot to straightaway center field leading off the fifth. He made his big league debut on Wednesday, got his first hit on Thursday and first RBI on Friday.
Fogg followed with a single. Helton reached with one out when Barfield, the second baseman, bobbled his grounder for an error. Holliday gave Colorado a 5-3 lead with his two-out double into the left-field corner on a full-count pitch from Williams.
Russell Branyan pulled San Diego to 5-4 with two outs in the sixth, hitting a 430-foot homer into the Padres' bullpen beyond the fence in left-center off Tom Martin.
- It was Colorado's second straight road win after snapping a nine-game road losing streak.
- Last month, the Rockies lost six straight games, then took two of three from the Padres in Denver.
- The Rockies recalled C J.D. Closser and purchased the contract of RHP Nate Field from Triple-A Colorado Springs. Field made his Rockies debut by striking out the first two batters in the seventh, making him the second Denver-born player in team history. The other was RHP Mark Knudson, who made four appearances in 1993.