SAN DIEGO >> Even when the Houston Texans fell behind by three touchdowns on the road in the second half of their season opener, Matt Schaub and Andre Johnson remained confident they could roar right back.

Sure, the San Diego Chargers were off to a solid start for their new coach.

The veteran Texans know how to finish.

Randy Bullock kicked a 41-yard field goal as time expired, and Houston rallied from a 21-point deficit in the second half for a 31-28 victory over the Chargers on Monday night.

“Once you put a score on the board, then another, and the defense gets a stop, the big turnover, it just builds,” said Schaub, who bounced back from an interception on Houston’s first play to pass for 346 yards. “Momentum keeps building, and you can feel that energy, and it’s contagious.”

Brian Cushing returned an interception 18 yards for the tying touchdown with 9:30 to play for the Texans, who erased a 28-7 deficit late in the third quarter to spoil the debut of Chargers coach Mike McCoy.

After two straight division titles and playoff trips, the Texans have ample experience in handling trouble together. Schaub provided steady leadership, and their vaunted defense held San Diego to 90 yards — just 7 on the ground — in the second half.

“There was no doubt in my mind that we were going to win that game,” said Johnson, who had 12 catches for 146 yards. “Even in the third quarter, we didn’t come out playing that great, but we got it together and made it happen.”

While the Chargers showed promise, the Texans began a season of Super Bowl aspirations with a gritty comeback befitting a defending two-time AFC South champion that got off to an 11-1 start last season.