They did, but that early lead was so big that they were still able to hold on for a 33-28 victory Thursday night.
"You're going up and down on the sideline screaming at everybody: 'Don't take your foot off the gas,'" Pagano said. "Next thing you know, just like that (it's close). It's never over in this league."
The Colts (4-2) led 24-0 after one quarter, but allowed Houston (3-3) to cut it to 33-28 early in the fourth quarter on J.J. Watt's fumble return for a touchdown.
"You give a team a 24-point lead right out the gate, you're going to have a difficult time," Watt said.
The Texans had two opportunities to take the lead late, but the Colts recovered fumbles by Andre Johnson and Ryan Fitzpatrick in the last five minutes.
"You can finally start to see the type of defense that we envisioned a long time ago to go out there and do that week in and week out," Pagano said.
Luck finished with 370 yards passing and three touchdowns for his fourth straight 300-yard passing game and T.Y. Hilton had a career-high 223 yards receiving with a touchdown to give Indy first place in the AFC South.
"We realized with the recent history of Thursday night games, teams who are going on the road are struggling, and we didn't want to do that," Luck said. "We were lucky enough to get off on that fast start. It takes focus, and you almost have to trick yourself into it."
The Texans were driving with less than five minutes remaining when Johnson — called for pass interference two plays earlier — caught a 13-yard pass and fumbled.
Watt knocked down Luck's pass on third down on Indy's next drive to give Houston one last chance. But Bjoern Werner sacked Fitzpatrick and stripped the ball and D'Qwell Jackson recovered.
"I was trying to make a play ... just poor ball security," Fitzpatrick said.
Fitzpatrick threw for 212 yards and a touchdown and Arian Foster had 109 yards rushing with two scores for Houston.
Indianapolis led by 12 when Luck fumbled and Watt recovered it and returned it 45 yards for a touchdown. It was Watt's third touchdown this season. He also has scored on an interception return and a reception.
Foster had a 34-yard run before Johnson grabbed a 26-yard reception to get Houston down to the 2 in the third quarter. Foster ran wide before cutting back inside and into the end zone untouched on the next play to get the Texans to 27-21.
The Texans were within six points in the third quarter when Luck, who was under heavy pressure, threw a 33-yard touchdown pass to Hilton. The 2-point conversion failed, leaving Indianapolis up 33-21.
After a dreadful first quarter where Houston managed just 2 yards, the Texans' offense finally got going in the second quarter. They kicked a field goal on fourth-and-5, but the Colts got a penalty to give Houston a new set of downs.
They took advantage of the opportunity when Fitzpatrick found Johnson in the corner of the end zone and he managed to get both feet in bounds for a 4-yard touchdown two plays later to cut the lead to 24-7. It was the first touchdown of the season for Johnson.
Houston got the ball back when Jared Crick tipped a pass by Luck that was intercepted by Justin Tuggle.
The Texans got to 24-14 when Foster scored on a 12-yard run.
The Colts added field goal to make it 27-14.
Luck found Hilton on a 40-yard pass early in the first quarter, but Indy's offense stalled after that and the Colts settled for a field goal to make it 3-0.
Trent Richardson had a 5-yard touchdown run on a two-play drive that included a 49-yard pass to Hilton.
The play was originally ruled a touchdown after Hilton recovered from a fall seemingly untouched by defender Kareem Jackson and reached the end zone. The play was reviewed and the call reversed, with Hilton ruled down by contact at the 5.
The Colts pushed the lead to 17-0 when Ahmad Bradshaw scored on a 5-yard pass from Luck with about seven minutes left in the first quarter.
The Texans had to punt again after Fitzpatrick was sacked by Werner for an 8-yard loss on third down after Bradshaw's score.
Luck capped a long drive with a 4-yard touchdown pass to Coby Fleener at the end of the first quarter to extend the lead to 24-0.
NOTES: Johnson finished with 99 yards receiving to give him 13,080 career yards receiving, making him the 15th player in NFL history to reach 13,000. ... Houston's Shane Lechler set a franchise record with a 71-yard punt in the third quarter.