Neither side had to wait long for their first touchdown of the match, but it was the Chargers who went over first when Philip Rivers picked out Bruce Matthews on a wheel route, before he caught the ball in his stride to walk it into the endzone.
The hosts extended their lead further in the third quarter when Rivers and Royal again combined to give the Chargers a 21-point advantage.
However, the Texans responded with five minutes left of the quarter through Garrett Graham after a terrific drive from Schaub.
The visitors then wiped clear a 14-point deficit with nine minutes left to play after Daniels and a Brian Cushing interception touchdown tied the match in the final quarter.
With just over a minute to play, the Texans moved into field goal range, which allowed Bullock to step up and nail a 41-yard field goal between the posts to win the match for the away side with just five seconds left on the clock.