The home run to right field was not only Headley's 27th of the season, a career high, but with that one momentous swing it allowed him to eclipse the 100-RBI mark -- he now leads the National League with 102 RBIs -- for the first time in his big league career.
"It was a great feeling," Headley said. "Obviously, that's a number along the way that means quite a bit."
Not nearly as much to the D-backs, who two days ago saw the Padres third baseman hit two home runs and drive in four runs in a victory. And then on Sunday, it was one swing that turned a tight game into a runaway, as San Diego (66-75) took two of three games from the D-backs (69-72).
"This series, the two games we lost, Headley, he hurt us," said D-backs manager Kirk Gibson. "Two home runs in the first game, grand slam today."
Headley, the reigning National League Player of the Month, has knocked in 60 runs in the second half -- tying him, oddly enough, with his current hitting coach, Phil Plantier, for the second-most RBIs in the second half of a season by a Padre. Plantier reached 60 in 1993, whereas Headley has 21 games remaining.
"He's found that feeling," Plantier said of Headley.
Headley wasn't the only story Sunday, though he was clearly the biggest.
Rookie left-hander Andrew Werner (2-1) pitched his fourth quality start in as many games, allowing one run on four hits with three walks and six strikeouts in 6 1/3 innings.
Werner walked a tightrope early in the game and allowed his only run on a double and two walks in the third inning. But he struck out Justin Upton looking to end the threat and essentially coasted from there, retiring the next 11 hitters he faced before leaving with one out in the seventh inning.
All told, Werner got 10 ground-ball outs in the game.
"The first three innings, he wasn't quite on the mark, you saw the elevated pitch count," said Padres manager Bud Black. "Then Andrew, for whatever reason, got back in the strike zone. I like the way he ended it. The fourth, fifth and sixth [innings] were really solid."
Werner, who has a 2.59 ERA after his first four Major League starts, wasn't pleased with his inefficiency in the early going.
"For whatever reason, I wasn't sharp, I had 60 pitches through three and I wasn't very efficient," he said. "The last three [innings] were pretty good."
The last three or so months have been very good for Headley, who celebrated the passing of the July 31 Trade Deadline -- he was a hot topic and target of opposing teams -- by going on a tear, the likes of which he hasn't seen or come close to approaching before this season.
There's been a few. Headley spoke at the end of last season about becoming more of a run producer. And to that end, he and Plantier worked as far back as January at Headley's home in Tennessee on philosophy and mechanics. One of the things that these two worked on was creating more loft in his swing, especially from his pull side (Headley is a switch-hitter).
"We're seeing aggressive swings earlier in the count, taking the at-bat to the pitcher," Black said. "He's being the aggressor. In previous years, they attacked him. Now he's attacking them."
In all, it has been a gratifying run for Headley, who before this season had never hit more than 12 home runs in a season or knocked in more than 64 runs. On Sunday, he surpassed the Brewers' Ryan Braun for the league RBI lead. Headley has been successful on the road and also at spacious Petco Park.
"When you focus on something and work on something and to get those results, that's a great feeling," Headley said.