TULSA, Okla. — Tristan Thompson knows he has one shot to make a first impression that sticks. One first, best chance to get in the other guy's mind like a nagging doubt that never leaves.

When his man rises for his first shot of the game, Thompson wants to be there. Whether it's with a full hand, a few fingers or a well-timed flick, Texas' freshman forward plans to swat that first shot away. Thompson's already learned that sometimes it's the first shot that matters most.

That thought almost seems contrary to everything the NCAA Tournament is all about at first blush. After all this is the tournament of buzzer beaters, the one-and-done masterpiece of chaos where anything can happen, the stage where tycoons find real heartbreak (Louisville's Rick Pitino) and work harder than they ever thought to avoid it (Kansas' Bill Self, who coaches on after Boston University's pesky fight Friday night). But a 20-year-old Canadian turned Texan knows better.

"It's a psychological thing," Thompson says, standing in the Texas locker room after the Longhorns' tourney-opening 85-81 turn back of 13th seed Oakland University. "I do try to always get the first one. Because if you block a guy's first shot, he's thinking about you all game."

Oakland University center Keith Benson isn't just thinking about Thompson — he probably ought to start charging Texas' big man rent for all the space he's taking up in his cranium. Thompson got Benson's first one and a 6-foot-10 NBA prospect suddenly started shrinking in front of 12,000 pairs of eyes at the cozy BOK Center.

If you don't think that changed everything, you weren't paying close enough attention. Truth is that the outcome of No. 1-seed Kansas' 72-53 win over 16th-seed BU was in doubt for much longer than the Texas-Oakland game, regardless of how different the final margins ended up being or how loud the Austin alarmists cry.

But now Texas faces a near-pro — and he'll be a lottery pick whenever he wants — at the art of the blocked shot and the mind games that go with it. Arizona sophomore forward Derrick Williams is as built as Thompson is lanky. More importantly, he's already a master at the killer timing that Thompson is still developing.

Sure, sometimes it's the first shot that matters most. But sometimes it's the last. Sometimes, the best player on the floor simply has to save the game.

That's what Williams did to set up fifth seed Arizona's super Sunday matchup with Texas. He swooped in and went after Memphis guard Wesley Witherspoon's once-open shot in the frantic, final seconds, went after it with authority after a rebound off a missed free throw gave the Tigers an improbable chance and threatened to turn Arizona coach Sean Miller's fouling-up-three strategy into disaster.

Williams got there though. Memphis' great shot traveled less than a foot, met meaty palm.

Arizona 75, Memphis 73.

"I just went up and made a hard play on the ball," Williams says.

Williams' play shows a breathtaking display of talent. But don't miss the brain behind it. In that end-game mayhem, when a lot of people around him were freaking out, Arizona's game changer made a calculated decision in an instant.

"Honestly with a second or two left on the clock, most refs don't call that type of foul, especially when you're trying to make a hard play on the ball," Williams says. "Earlier in the game, they might have called a foul because (Wesley) did fall to the ground. But late in the game, most refs don't call that."

Williams knew that the referees didn't want to decide the game. So he did.

Arizona's lifeline probably didn't realize that Jim Burr, the same official who was part of the crew that infamously botched the end of the Rutgers-St. John's game earlier this month, was under the basket for the fateful non-call. But Derrick Williams leaves little else to chance.

On a night when Memphis' bright, boyish coach Josh Pastner threw a box-and-one and a triangle-and-two — almost unheard of defensive strategies against a big man — at Williams and took the best player out of the game at times, Williams still finished with 22 points and 10 rebounds. He still made the plays that won the game.

A huge late 3-pointer. The block that ends it.

"There is a reason why I voted Derrick Williams National Player of the Year," Pastner says.

A Force Awakening?

Thompson isn't on top of anyone's Player of the Year ballot. But he's coming fast. His teammates saw what Benson was in for long before the unassuming Oakland University player did.

For in the days before Texas' first game in the NCAA Tournament, the freshman asked for the biggest defensive assignment. He wanted Benson. One on one. Don't you dare think of sending any double teams. He's mine.

"You don't see a freshman doing that," Texas forward Jordan Hamilton says.

"He was pretty insistent too," Texas forward Gary Johnson chuckles. "He knew Benson had been talked about as an NBA player. Tristan was going to be mad if coach sent any double teams."

Rick Barnes didn't send any double teams. The Longhorns coach never even had to think about it. Not with Thompson jumping around in Benson's head.

"I knew about his shot blocking ability," Benson says. "I don't think it surprised me. It just happened."

Just like Williams just happened to Memphis. That's what the best players do in March. Game changers prevail in the NCAA Tournament, big school or small. All the better if you can do it with the block.

There is no more intimidating play in basketball. Nothing shakes a confident player more than getting his shot swatted back in his face.

Thompson wants Williams' first shot on Sunday. But Texas has to be wary that Williams will deliver the last one.

"It's funny because we've been on Tristan a little this year about guys having good games against him," Johnson says. "We kid him a lot. He was determined to make sure we couldn't say anything today."

Shot blockers don't need to listen to outside noise. Not as long as they're in their man's head.