"Sometimes it takes something little like that to get you going," Headley said. "You get the momentum going in you favor and big things can happen. That [Amarista's hit] jump-started that inning for us."
The Padres, returning home after a 1-9 road swing to St. Louis, New York and Chicago, didn't have much in the way of offense against D-backs starting pitcher Wade Miley (6-2), who entered that eighth inning having allowed one run on three scant hits.
After getting the first out of the inning, the left-handed-hitting Amarista dropped down a bunt that gave him more than enough time to cover the 90 feet coming out of the box, so much so that first baseman Paul Goldschmidt, who picked up the ball, didn't even bother with a throw.
San Diego manager Bud Black went to his bench for Guzman, who came up empty in two critical pinch-hitting opportunities earlier in the week against the Cubs. This time, though, Guzman jumped all over a changeup that Miley left up in the strike zone, sending into the left-field seats for his first home run of 2012.
"It's way different here," Guzman said of Petco Park, where he was able to get some swings in before his pinch-hitting appearance. "Here, we've got a cage. At Wrigley, we had no cage."
Guzman's home run was the second pinch-hit home run of the season for the Padres. Mark Kotsay had one on May 1 against Milwaukee.
"'Guzie' was due to do something big," Black said. "We saw it a lot last year. 'Guzie' is a good hitter."
The Padres (18-35) kept on scoring as Cameron Maybin had an RBI triple, Carlos Quentin had an RBI single and Nick Hundley added a sacrifice fly. Quentin is now 8-for-16 with seven RBIs in four games since returning from the disabled list.
"That was a good one," Black said of the inning. "We had some good at-bats. I like the way we added on."
More than that, there was plenty of good pitching.
San Diego pitcher Clayton Richard allowed one run on seven hits over 6 2/3 innings. He walked one and struck out three. Better still, he pitched his way out of trouble in the second and fourth innings when he allowed the leadoff hitter to reach base.
"That was a time in the game where things could go either way, and we were able to make some pitches and get out of it," Richard said.
Richard left the game in the seventh inning with runners on first and second base. But Luke Gregerson got Aaron Hill on a ground ball to Amarista at second base to end the inning.
"He was hitting his locations," D-backs shortstop Willie Bloomquist said of Richard. "He threw his changeup effectively and had a cutter in there, too. We put some hits up, but we didn't put a whole lot together at the right times. It was unfortunate."
Andrew Cashner (3-3) pitched a scoreless, though interesting, eighth inning. Cashner missed inside on a 3-2 pitch to Chris Young, who had to lean back to get out of the way of the pitch. As he walked to first base, Young -- glancing to third-base coach Matt Williams for signs -- exchanged words with the Padres reliever. The benches cleared but order was restored quickly.
With the loss, the D-backs fell to 23-29.