After two fly balls to end the first, the Padres didn't hit the ball beyond infielders through the fifth. But the game unraveled after a five-pitch walk to Padres starter Trevor Cahill.
Manuel Margot tripled past a sliding Charlie Blackmon in center to drive in Cahill.
"It was a 2-0 pitch right down the middle, Charlie made a good effort and it got by him," Chatwood said. "Can't really do anything about that."
Two batters later, Wil Myers doubled on a ball that Blackmon's angle didn't help him get close to, then Yangervis Solarte and Ryan Schimpf homered.