The Diamondbacks will try to snap a seven-game skid against the Padres on Saturday night when the teams continue their three-game series at Petco Park.
While Arizona has significant ground to make up in both the NL West and wild-card race, it created some momentum for itself earlier this week after taking two of three from division-leading San Francisco.
However, the Diamondbacks (68-71) continue to come up short against the Padres, losing 6-5 Friday. Headley drove in four runs on two homers, including a tiebreaking solo shot to lead off the eighth as Arizona dropped 10 1/2 games behind the Giants again.
The Diamondbacks are 4-9 against the Padres, but 23-16 against the rest of the division. They've been outscored 48-25 during a seven-game skid in the series.
"It seems like things happen every time we play them," said rookie starter Tyler Skaggs, who allowed five runs in three innings.
Like most of the NL, the Diamondbacks haven't found the answer to Headley, who is hitting .357 (10 for 28) with 10 RBIs during his team's winning streak against Arizona.
The Diamondbacks are in good company, however. Headley is hitting .361 with seven home runs over the last 20 games and is 17 for 42 (.405) in his past nine with four homers.
"Headley's on fire," Arizona manager Kirk Gibson said. "We know that. You just have to make good pitches. If you don't make good pitches, he's going to pound you like he did tonight."
In large part because of Headley, San Diego (65-74) has won three straight and 13 of 17. It has also won 17 of 22 at home.
The Padres will try to keep things going against Wade Miley (14-9, 2.90 ERA), who has a 2.28 ERA over his last four starts.
Miley went 6 2-3 innings against the Los Angeles Dodgers on Sunday, allowing three runs and nine hits in the 5-4 loss. He was in line for the win before closer J.J. Putz gave up two runs in the ninth.
The left-hander had one of his worst starts of the season against the Padres on June 1, yielding four runs in 7 1-3 innings of a 7-1 defeat. Miley has given up more than three earned runs only five times in 24 starts.
He'll be opposed by Casey Kelly (1-0, 3.86), who will make his third start for the Padres.
After going six scoreless innings in his major league debut against Atlanta on Aug. 27, the 22-year-old right-hander allowed seven runs - five earned - in 5 2-3 innings of an 11-10 loss at Colorado on Sunday.
All seven runs came in the third inning, when he faced 11 batters. San Diego manager Bud Black said he was pleased with how the rookie settled down after that.
"That says a lot about Casey," he told the Padres' official website. "He wasn't rattled. He kept battling. He just went out there and kept pitching."