Padres catcher Nick Hundley and manager Bud Black weren’t around to watch the impressive finish, both thrown out by home plate umpire Eric Cooper in the bottom of the sixth.
Henry Blanco, who had replaced Hundley, led off the 10th with his second single, then Headley hit a 1-1 pitch from Tony Pena (4-2) some 130m off a sign above the swimming pool in left-center.
DODGERS 16, ROCKIES 6
At Denver, James Loney, Russell Martin, Juan Castro and Matt Kemp had three hits each as Los Angeles used two big innings — a seven-run fourth and an eight-run seventh — to rout Colorado.
Juan Pierre had a bases-loaded triple for the Dodgers, who matched their season high with 19 hits.
Will Ohman (1-0), the third pitcher for Los Angeles, picked up the win.
Brad Hawpe had two doubles and three RBIs for the Rockies. Jorge De La Rosa (0-5) took the loss.
REDS 8, ASTROS 5
At Cincinnati, Jonny Gomes had three RBIs and Cincinnati made the most of three Houston errors, scoring eight unearned runs.
Gomes had three hits for the Reds, who have won three of four.
Jerry Hairston Jr, Ramon Hernandez, Adam Rosales and starter Aaron Harang (5-4) had two hits apiece.
Lance Berkman hit a two-run homer for Houston.
In other NL games it was:
• Giants 8, Braves 2
• Marlins 5, Phillies 3
• Mets 5, Nationals 2