• Statistics | Photos from Reliant Stadium

After blowing Sunday’s game to the San Diego Chargers, the Texans are wallowing in a pit of mediocrity at the midway point of the season.

The euphoria over the Texans’ 2-0 start has disintegrated into the despair of a 4-4 record, including 2-3 at Reliant Stadium, where they allowed the Chargers to overcome a nine-point deficit and escape with a 29-23 victory.

This game had a little of everything, including questionable play calls by the Texans, controversial calls by the officials, blown opportunities in the red zone by the offense and another embarrassing performance by a secondary that allowed four touchdown receptions to backup receivers.

It was a wasted opportunity against a team that was 0-4 on the road. A victory would have given the Texans a 5-3 record and a three-way share of first place in the AFC South going into the next two games on the road against Jacksonville and the New York Jets.

“Frustrating doesn’t begin to describe what I’m feeling right now,” middle linebacker Brian Cushing said. “It’s super-frustrating because we just gave the game away. We knew exactly what they were going to do — deep balls for big plays — and we couldn’t stop them.”

To put this game in perspective, consider the Chargers’ injury-ravaged offense was missing its three leading receivers and tight end Antonio Gates. Then they lost running back Ryan Mathews to an ankle injury in the first half.

No matter who he had in the huddle, quarterback Philip Rivers still managed to torch the Texans’ secondary for four touchdown passes. Two went to rookie receiver Seyi Ajirotutu, who plays behind Vincent Jackson (suspended), Malcolm Floyd (injured) and Legedu Naanee (injured).

‘It’s painful’

Rookie cornerback Kareem Jackson was burned for 55- and 28-yard touchdowns by Ajirotutu, the latter of which proved to be the game- winner.

“It was tough,” said Jackson, who also intercepted his second pass of the season. “Any time that happens, you don’t give your team a chance to win. It’s painful, but you have to do everything you can to get better. I’m mad at myself, but I’m going to use it as a learning experience.

“I’m a rookie, which is not a reason for my play, but at the same time, the other team watches film. Anytime they see on film you’re giving up the deep ball, of course they’re going to attack it.”

Rivers, who finished 17-of-23 for 295 yards, threw his other two touchdown passes to backup tight end Randy McMichael.

“We’re not good enough to have any breakdowns,” outside linebacker Kevin Bentley said.

The Texans wasted Arian Foster’s 127-yard, two-touchdown performance against the NFL’s second-ranked run defense. They entered the game ranked first in the red zone, where they were 2-for-6 against the league’s top-ranked defense.

“This one hurts deep,” cornerback Glover Quin said. “We had a team on the ropes. We had them down, and as a defense, we couldn’t finish. As a defense, we couldn’t hold on. We let this one slip right through our fingertips.”

Foster ran for 99 yards and two touchdowns in the first half, when the Texans scored a season-high 20 points and led by six. They could have scored 24, but Foster dropped a touchdown pass when he didn’t control the ball in the end zone. They had to settle for one of Neil Rackers’ three short field goals.

“It’s disappointing, because you can’t put field goals against a team like that with a high-powered offense,” Foster said after recording his fifth 100-yard game and regaining the league lead in rushing and yards from scrimmage. “They teach you to have a short memory in this game, and you have to shake it off and come back.”

Like the Chargers did.

The Texans led 23-14 in the third quarter and 23-21 in what turned into a wild, controversial fourth quarter.

Kubiak went for it on fourth down two times in the fourth quarter, and Foster and quarterback Matt Schaub were stuffed at San Diego’s 17- and 34-yard lines.

“You always regret it when it doesn’t work,” Kubiak said.

Schaub was called for intentional grounding when he threw in the direction of tight end Joel Dreessen, but all the huffing and puffing by the players and coaches couldn’t get referee Mike Carey to change the call.

Two plays later, Schaub was stopped on his fourth-down sneak, which needed 11

2 yards.

Last chance fails

Still, the Texans had one last chance to pull out a victory when they got the ball at their 14 with 3:06 left. Schaub completed four passes, including a screen that Foster turned into a 33-yard gain. A play later, the Texans had a second-and-10 at the San Diego 28.

With 1:34 and one timeout remaining, Schaub threw over the middle to Andre Johnson, who couldn’t handle the pass, and the ball bounced off his knee to strong safety Paul Oliver, who reached down for the interception that instant replay upheld.

“To be 2-3 at home and 2-1 on the road is baffling,” outside linebacker Zac Diles said. “Since I’ve been here, we’ve been a great home team, and we’ve never really given up big plays like that. It’s disheartening.”

john.mcclain@chron.com