ARLINGTON, Texas — It’s all true: Oklahoma doesn’t play good defense. The numbers don’t lie.The Sooners have labored to stop opposing offenses for most of the last decade, let alone the 2018 season. Things reached record levels when Mike Stoops returned as defensive coordinator in 2012, then got steadily worse, and haven’t been appreciably better since Stoops was fired this past October. But has the Playoff spot been secured — or even considered?”We’ve beat everybody on our schedule,” Riley said. “I feel like we can score points on people and I feel like we can stop people and . . . I feel like we’re gaining traction defensively.”I know we can. I have zero doubt.” But something has clicked these last two weeks, something impossible to quantify: Just when it looked as though the Sooners’ porous defense would finally get them beat — it happened that steamy day in Dallas back on Oct. 6, after all — someone rises up and makes a winning play.MORE: SN’s live blog of Oklahoma-Texas title game Last week, it was two defensive touchdowns in a three-point win at West Virginia.This week, it was three straight defensive stops in the fourth quarter, punctuated by a lightning-strike blitz for a safety and a goal-line interception to preserve the Sooners’ 39-27 victory over Texas in the Big 12 championship game.”There’s no doubt there’s been things we have needed to do better,” coach Lincoln Riley said after the game. “We haven’t run away from that. But we’ve also felt a lot of confidence of the coaches and players in that room that they would step up when it mattered most.”When it mattered most, Tre Norwood broke up a pass from Sam Ehlinger to Lil’Jordan Humphrey on third-and-9. When it mattered most, Ehlinger was sacked in the end zone on a corner blitz by Tre Brown. And when it mattered most, Norwood picked off Ehlinger’s final throw with 51 seconds to play, setting off a shower of confetti and another trophy presentation and, well, plenty of horns down.”For many people on the outside, they would say our defense is the worst in college football,” said OU wideout CeeDee Lamb, who had 167 yards and a touchdown. “But for them to come up and make that big play at the time we needed it, that’s the most valuable play to me.”Was it a good enough showing to move the Sooners up from No. 5 and into the College Football Playoff’s top four? The answer won’t be known until Sunday morning, but with Alabama’s come-from-behind win against Georgia in the SEC championship game. . . .Beating No. 14 Texas at AT&T Stadium probably keeps Oklahoma ahead of No. 6 Ohio State, regardless of the Buckeyes’ outcome against No. 21 Northwestern in the Big Ten championship game, but even that’s not a certainty. OU improved to 12-1, avenging its only loss of the season, while Texas fell to 9-4.Kyler Murray threw for 379 yards and three touchdowns without an interception, but the Sooners’ ground game was curbed and go-to receiver Marquise Brown suffered a case of the drops before an injury knocked him out of the game.The Oklahoma offense was sputtering a bit, comparatively speaking.That’s why Oklahoma’s defense stepping up at the right time was so important to the Sooners winning an unprecedented fourth straight Big 12 title and the program’s 12th overall. (By comparison, Texas owns the second-most Big 12 championships. The Longhorns have three.)”Oh, man, the defense balled out today,” said running back Kennedy Brooks. “They put the team on their backs today.””It’s probably the reason we got the win,” said running back Trey Sermon. “They got a few key stops even when the offense wasn’t playing at a good level. Just them helping out, it was tremendous.”It was a moment of complementary football, the kind the College Football Playoff selection committee likes to talk about on Selection Sunday.Oh, Saturday’s game was rocky for the Sooners’ D — as usual. Texas’ opening drive was too easy, with Ehlinger hitting clutch throws on third-and-8 to Collin Johnson and third-and-10 to Humphrey, and then running for a 16-yard touchdown on third-and-1. It was easy again in the second quarter when Ehlinger converted a fourth-and-4 throw to Johnson to help Texas take a 14-6 lead.Murray and the Oklahoma offense, meanwhile, mustered only two field goals. It was the first time in 25 games the Sooners were held without a first-quarter touchdown. OU continued to struggle at stopping Ehlinger (both running and throwing), but the Texas running backs found no space against an unexpectedly stingy defense. Ganging up against the run may have given the Sooners confidence to finish strong.”We obviously didn’t make enough plays down the stretch,” said Texas coach Tom Herman. “That’s a heck of a football team that they have there with an unbelievable offense.”Trailing 14-6, Murray finally caught fire in the final seven minutes of the second quarter, completing 7 of 7 throws for 147 yards and two touchdowns on the final two drives before halftime to put the Sooners ahead 20-14. On the opening drive of the third quarter, Murray was 3 for 4 for 30 yards and Sermon’s touchdown gave OU a 27-14 lead.Against a defense that has been historically bad, however, that lead wasn’t enough. Ehlinger drove Texas to back-to-back touchdowns — again, too easy — and it was 27-27.Austin Seibert’s 31-yard field goal ricocheted off the left upright and in for a 30-27 OU lead, and that’s when Oklahoma’s defense stepped up.MORE: Watch college football live on fuboTV (7-day free trial) After a punt, OU looked ready to extend its lead when Lamb zig-zagged into the red zone on a 46-yard catch-and-run from Murray, but Gary Johnson’s big hit from behind separated Lamb from the football and Texas took over at its 8-yard line.At that moment, Brown delivered arguably the play of the game, a situational blitz from his cornerback spot that neither Ehlinger nor his blockers saw coming. Brown smashed into Ehlinger in the end zone for a safety, giving the Sooners a 32-27 lead and the ball back with 8:19 to play.Murray converted a third-and-6 with an 18-yard completion to Lee Morris and a third-and-9 with a 13-yard throw to Morris, and then saved his best for last — a nuanced, 18-yard fade throw against an all-out blitz on third-and-10 to tight end Grant Calcaterra, who made an outstretched, one-handed snag in the back of the end zone for a 39-27 advantage.”That catch will live on in Oklahoma history forever,” Riley said. “What a play.”Game over. Championship secured.