HOUSTON — Cam Skattebo was back to back-flipping.

One week after he was minimized with no touches as punishment for his fumbling problem, Skattebo powered his way to a tie-breaking 16-yard fourth-quarter touchdown — and set up Devin Singletary’s walk-off 30-yard touchdown run in overtime as the Giants upset the Texans, 27-21, at Reliant Stadium.

In his first start of the season, J.J. McCarthy threw lasers on the way to 252 yards but the Giants scored had four different ball-carriers score on the ground to win as 10-point underdogs.

Skattebo’s 42-yard rush in overtime ended with him sliding to the ground after a potential hamstring injury. Enter Singletary, a third-stringer former Texan, who juked Kamari Lassiter and broke free for a touchdown that stunned most of the crowd – except for the ones chanting “Let’s Go Giants!” in the fourth quarter.

Skattebo capped his fourth-quarter touchdown with his signature backflip and hugged head coach John Harbaugh, who doled out the harsh penalty to his starter last week but went back to him. The Giants moved 80 yards in 14 plays, converted three third downs and a fourth down, and took 8:18 off the clock.

The Giants also tackled Harbaugh in celebration after Singletary’s score.

The Giants (4-2-1) have won six straight in the series since losing during to the Texans’ 2002 expansion team. They are in command of a weak NFC East after proving it was foolish for the underachieving Texans (2-5) to be big favorites.

Defensive coordinator Dennard Wilson looked mostly wise after his unit responded to a challenge to give better effort hustling to the ball and his usage of “traitors.”

The Giants forced punts on three straight second-half possessions, but the gift of starting field position across midfield allowed the Texans to score the game-tying touchdown with 52 seconds remaining.

After the Giants went nowhere on their final possession of regulation, the defense atoned with a three-and-out. Kayvon Thibodeaux dropped an interception thrown run onto his hip.