The defending champions are 48 minutes from elimination.

The Oklahoma City Thunder put a pounding on the Dallas Mavericks that likely has signaled a changing of the guard in the Western Conference. The Thunder's 95-79 romp Thursday has the young upstarts one victory from advancing to the second round.

The Mavericks, down three games to none in the best-of-seven opening-round series, at this point are just looking to extend their season Saturday night home at American Airlines Center. It's a long fall for a franchise that climbed the NBA mountain last June.

"It's really tough to go down 0-3," Dallas coach Rick Carlisle said, "but we're going to keep fighting."

Kevin Durant and the rest of the Thunder began their ascent to legitimate title contenders last year. That season ended in the West finals at the hands of the Mavericks.

Oklahoma City hasn't avenged that postseason loss ... yet.

"We just play. We just play hard basketball," Thunder coach Scott Brooks said. "We play as hard as we can, and we live with the results. We don't get caught up in things we can't control.

"We know that they have the heart of a champion."

Durant might have ripped it out by scoring 21 of his game-high 31 points in the first half. The third quarter is what won it for the Thunder.

Oklahoma City turned a nine-point halftime lead into an insurmountable 18-point edge going into the final 12 minutes. Russell Westbrook scored 11 of his 20 points in the third.

In a game that Dallas guard Jason Terry called their "Game 7," there hardly seemed to be a sense of urgency from the Mavericks. Franchise icon Dirk Nowitzki sloshed his way to 17 points, unable to shake free of Serge Ibaka and the rest of the Thunder's active defenders.

"This was a Game 7 for us," Oklahoma City sixth man James Harden countered. "We needed it, it was a must-win for us, and we came out with that intensity. Same thing for next game as well. They're the defending champions, and they're just not going to lay down. We got to come out from the beginning."

Whatever momentum the Mavericks had at the end of the first quarter, Oklahoma City snatched it back in the second. The Thunder's youth and athleticism was evident at both ends of the floor.

However, that's not to say the visitors were without some veteran poise. A dynamic 28 seconds late in the second period thrust the Thunder back in control.

Derek Fisher, as he's done countless times over his postseason career, drilled a wide-open 3-pointer from the corner. Westbrook followed with another 3-pointer.

Westbrook cooled off his guns/hands like he an Old West gunfighter and stuck them back in the holster. The Mavericks called timeout. Oklahoma City was up 48-33.

The Mavericks did close the gap to 50-41 at halftime despite shooting just 37 percent. Nowitzki had 10 points but uncharacteristically missed two free throws. Jason Kidd also had 10 for the defending champs.

Westbrook, Harden and Ibaka each scored eight apiece in the first half to support Durant.

The Thunder's aggressiveness early put Dallas on its heels. Oklahoma City scored the game's first six points and led 16-7 less than five minutes into the contest.

Durant carved up Shawn Marion in the first quarter, scoring 15 points on the man Carlisle called the league's best perimeter defender.

Carlisle wasn't happy later in the quarter, picking up a technical foul after Thunder center Kendrick Perkins worked inside to tip in a missed shot.

Carlisle erupted on the sideline and had to be restrained by assistant Terry Stotts.

"Frankly, a lot of the responsibility is on me," Carlisle said. "I didn't have these guys ready to play."

The tirade must have lit a fire under the Mavs, as they finished the quarter on a 13-4 run to trail 32-26. Vince Carter paced Dallas with seven points off the bench in the period.

NOTES: Thunder sixth man Harden has been added to the list of finalists for the 2012 USA Olympic team. Durant and Westbrook are also finalists. ... Kidd won the NBA Sportsmanship Award, the league announced. The NBA will donate $10,000 to the Jason Kidd Foundation, which aids children's educational causes. ... Carlisle has thought play in this series has been dirty at times, but has it been physical? "Compared to the '80s? No," he said. "It's a little physical." ... The Mavericks have never been swept in a best-of-7 series.