The Texans (1-0) found themselves down 28-7 early in the third quarter, but went on to outscore the Chargers 24-0 the rest of the way to pull off an improbable comeback.
Matt Schaub was 34-for-45 passing for 346 yards, three TDs, with one interception. He hit Garrett Graham with a seven-yard scoring pass and later found Owen Daniels on a nine-yarder with 14:44 remaining, cutting the deficit to 28-21.
Then with 9:30 left, Brian Cushing picked off a Phillip Rivers pass and rambled 18 yards for another touchdown, forging a 28-28 tie.
On final drive, Schaub marched Houston 38 yards on nine plays, setting up Bullock's game-winning kick as time expired.
Andre Johnson gained 146 yards on 12 catches while Daniels finished with two touchdowns on five grabs for the Texans.
Rivers completed 14-of-29 passes for 195 yards and four TDs for the Chargers (0-1), who also blew a big lead against Houston in a loss last season.