"[Chapman's] a guy that's throwing the ball with so much velocity, so you've really gotta narrow it down and get the barrel to it," Headley said. "He's one of those guys that if you're able to get the barrel to it, he's throwing so hard, that it really supplies some power for you. I was just trying to get on top of a fastball, so fortunately, I hit it well enough and it went out."
"Just one pitch," said Cincinnati catcher Brayan Pena of the ball Headley hit out. "We left it a little bit up, and it really cost us the game."
Before Headley's fourth homer of the season, which came on a 1-1 count, the contest had been a pitchers' duel, with Padres ace Andrew Cashner locked in a battle with the Reds' Mike Leake. The right-handers gave up just one run each, but neither figured in the decision.
Cashner -- who before the fourth inning Tuesday had gone 21 consecutive innings without a run of support -- scattered seven hits over seven innings. He walked one and struck out six in his 13th quality start in his last 16 outings dating back to August.
"I thought I had good stuff," Cashner said. "I hadn't been throwing as many breaking balls leading up to this, and I thought my breaking ball was better tonight, and I located my fastball."
The only run Cashner allowed came in the first inning, when Billy Hamilton led off with a triple down the left-field line and scored two batters later on a single to right by Brandon Phillips.
Cashner got into a jam in the sixth, when Phillips led off the frame with a double, Joey Votto followed with a walk, and one out later, Ryan Ludwick reached on catcher's interference as Rene Rivera's glove interfered with Ludwick's swing.
With the bases loaded and one out, Cashner got Chris Heisey to ground softly back to the mound, enabling Cashner to get the force at home. Cashner then got Zack Cozart to pop out to first to end the threat.
"They made me make pitches; they're a good-hitting team," Cashner said. "I think that whole [sixth] inning started with a bad slider to Phillips. I think I had a couple of close pitches to Votto, and I kind of tried to work around him and tried to put him on base. And then I had to go to work after that."
Go to work he did, and it proved crucial in giving the Padres a chance to win the game late.
"It was critical, no doubt about it," Padres manager Bud Black said. "It was a turning point in the game. … Bases loaded, one out, they're stressing [Cashner]. His pitch count was climbing that inning, and he had to work awful hard. But he made some pitches, he really did. … For us, that was the game, no doubt about it."
San Diego's lone run before the ninth scored in the fourth, when reigning National League Player of the Week Seth Smith led off the frame with a double and scored on a sacrifice fly by Jedd Gyorko.
Joaquin Benoit, who pitched the eighth inning, notched the win, his first of the season. Huston Street picked up his 12th save with a 1-2-3 ninth. Street has converted 37 of his last 38 save chances dating back to May 14th of last year.
The one-run victory was the Padres' Major League-leading 27th game decided by two runs or less, and in extended the Padres' win streak to four games, their longest of the season.