LOUISVILLE, Ky. (AP) -- Oklahoma coach Bob Stoops didn't mind trailing Louisville 13-7 at halftime.

He hoped to see how his squad would respond to adversity. It passed with honors.

Down 21-14 midway through the third quarter, the Sooners scored 28 unanswered points to pull away for a 42-21 victory Saturday and improve to 3-0 for the first time since 1995.

"I told our players (at halftime) that I was kind of pleased we were behind because I wanted to see what kind of fight we had," Stoops said. "I was pleased with the attitude of our guys in the second half. I think they knew a little more what they were doing and played with more confidence."

Josh Heupel tossed four of his five TD passes and ran for a 1-yard score in the second half to provide the offensive firepower.

The Oklahoma defense stepped up as well, picking off two second-half passes to keep the Cardinals' explosive offense in check.

Heupel, who was 29-of-42 for 429 yards, broke his week-old school record of 420 yards against Baylor. He connected on TD throws of 6, 11, 44, 52 and 52 yards and spread passes among eight receivers.

Michael Thornton also carried 17 times for 94 yards as Oklahoma, with the nation's third-ranked offense, racked up 544 yards against the Cardinals (2-2).

"We have to look at ourselves from here on out and just do better," Louisville coach John L. Smith said. "You can't play for a half and expect to win."

Louisville's Chris Redman, who has 10,198 yards to become the 14th major-college passer to throw for 10,000 yards, was 24-of-49 for 292 yards and two touchdowns with two interceptions. He was only 8-of-20 in the second-half for 77 yards.

Lavell Boyd caught six passes for 120 yards and Frank Moreau carried 21 times for 94 yards as Louisville's top-ranked offense was held to 386 yards, 157 below its average.

"In the second half, we seemed to fall apart," Redman said. "We have a good offense, but right now we're just a little slow."

Louisville led 13-7 at halftime on Jon Hilbert's 27- and 35-yard field goals and Redman's 22-yard strike to Zek Parker with 5:16 to play. The defense held tough despite allowing a 52-yard TD pass from Heupel to Josh Norman.

Even with the lead, Smith sensed something was wrong.

"I jumped around like a chicken with its head cut off and yelled, `Let's go play! Let's have fun! Let's show some excitement!"' Smith said. "But we didn't have any, and I don't know what the answer is."

Heupel hit Jarrail Jackson with a 52-yard scoring strike less than two minutes into the second half as Oklahoma regained the lead 14-13.

Later in the quarter, Redman hit Arnold Jackson with a 15-yard TD pass and the two-point conversion to go up 21-14. The Cardinals appeared ready to increase the lead on their next possession, but Rodney Rideau's interception in the end zone swung the momentum the Sooners' way.

"It's all about making plays when you get in the red zone," Redman said. "When you play good teams, you can't give away chances like we had down there."

From that point on, Heupel took over.

After the interception, he hit Damien Mackey for an 11-yard score to tie the game at 21. Following a Louisville punt, he found Mackey again for a 6-yard TD to regain the lead for good.

Another Redman interception on the Cardinals' next possession led to Heupel's first-ever rushing touchdown, a 1-yarder that gave the Sooners a 35-21 lead with 9:52 to play.

"It took me time to get going," Heupel said. "When I struggle, the offense usually struggles.

"You've got to capitalize on opportunities when teams give them to you. We took advantage of them in the second half."

Heupel ended his afternoon with a bang. On fourth-and-one at the Louisville 44, Heupel faked a handoff up the middle and lofted the ball down the left sideline to a wide-open Jackson for his fifth TD pass of the day.

"We know this offense can score points," said Mackey, who caught four passes for 48 yards and two touchdowns. "In the first half, we didn't execute. The second half, we executed a lot better and came up with the big plays."