Headley's second home run of the game, a tiebreaking shot to straightaway center field off of Arizona reliever David Hernandez in the eighth inning, gave the Padres (65-74) the lead for good in a game they once led, 5-0.
"The last couple of months, he's been in a great spot confidence-wise and swing-wise," Black said. "There's no doubt he's swinging the bat great from both sides."
In 136 at-bats since Aug. 1, Headley is hitting .338 with 14 home runs and 46 RBIs -- on 46 hits, no less.
For the month of September -- or all of six games now -- Headley has 15 RBIs in his first 28 at-bats. This, of course, comes on the heels of an August when he hit 10 home runs, knocked in 31 runs and was the National League Player of the Month.
Facing the D-backs (68-71), Headley had a three-run home run in the first inning hitting right-handed. His second home run, No. 26 on the season, a career high, was hit left-handed.
"That was a nice way to finish," Headley said. "I got up in the count 2-0 and got a little aggressive and I kind of overswung. It was nice to step out and rethink my approach at the plate."
Headley has four multi-homer games this season and has 98 RBIs, which puts him one behind Ryan Braun of the Brewers for the National League lead.
"Headley's on fire, we know that. We just got to make good pitches. You don't make good pitches, he's going to pound on them just like he did tonight," said D-backs manager Kirk Gibson.
The Padres needed each and every one of Headley's four RBIs on Friday, especially after the D-backs got back into the game after trailing 5-0 after three innings.
Arizona's Ryan Wheeler got the D-backs' comeback started with a two-run double off San Diego pitcher Andrew Cashner in the fifth inning. Wheeler would later add an RBI double in the seventh inning. Then, in the eighth inning, Miguel Montero hit a two-run RBI double off Tommy Layne to tie the game.
Cashner, making his first start since July 3, had four scoreless innings to start the game before allowing two runs in the fifth inning. All told, he allowed the two runs in five innings with no walks and five strikeouts.
Cashner was reinstated from the disabled list on Sept. 1 after he missed 51 games with a strained right lat muscle.
"I wanted to come out of it healthy and I wanted to locate my fastball," said Cashner, who finished with 68 pitches, 47 for strikes. "My changeup command was really good. I had a good feel for it and got guys out in front with it."
The Padres, who are 20-10 since Aug. 5, jumped out to a 2-0 lead in the first inning off D-backs rookie left-hander Tyler Skaggs as Yasmani Grandal lined a two-run double into the left-field corner. That allowed Chris Denorfia and Logan Forsythe, who had singled earlier in the inning, plenty of time to score.
Then in the third inning, Skaggs walked Denorfia and allowed a single to Forsythe. Headley then jumped on a pitch and hit it out to left field.
"I feel like two to three times a game, I'm coming up with guys in scoring position," Headley said.
Brad Brach, the seventh pitcher the Padres used, got the victory with a scoreless eighth inning. Reliever Luke Gregerson, filling in for injured All-Star closer Huston Street, got three outs in the ninth inning for his fifth save of the season.