The Phoenix Suns more than turned up their defense in their 101–81 win Tuesday night over the San Antonio Spurs — they changed the complexion of the series.

To be sure, the Spurs come back to the AT&T Center for Game 3 on Saturday and Game 4 on Monday having taken home-court advantage away from the Suns by winning Game 1, but before the series resumes, coach Greg Popovich and his assistants will need to spend a lot of time figuring out how to beat the Suns now.

With the Suns’ potent and turbocharged offense, Phoenix strikes fear into the hearts of most NBA teams, but before Tuesday, San Antonio had reason to feel confident playing against them. The Spurs had won 12 of the 16 meetings in the Mike D’Antoni-Steve Nash era, and it wasn’t hard to see why. In Game 1 of the series Sunday afternoon, the Spurs’ perimeter defenders stayed attached to their men, or shrewdly stayed in the passing lane between the interior ballhandlers and the Suns’ perimeter shooters. This kept the Suns from using the three-point shot as a weapon, and it’s a key to the Phoenix attack — they shoot 28.6% of their shots from behind the arc and their average of 24 attempts per game led the league for the third straight season. Also the Spurs cut off the Suns’ inside game, forcing Amare Stoudemire, the team’s all-star center, into a 6–19 shooting nightmare.

So pardon the Spurs if they thought Tuesday night would be more of the same. It wasn’t. The Suns finally owned up to a basic tenet of a short series: If an opponent takes away a facet of your game, then respond by taking away a facet of theirs. Although much attention has been devoted to the play of former Knick Kurt Thomas, who started and played well, Suns forward Shawn Marion has had the biggest impact on the game. Marion took the defensive assignment of guarding Spurs point guard Tony Parker and held him in check.

Parker had been the biggest key to the Spurs’ 111–106 Game 1 win. The point guard shot a sizzling 14–22 from the field en route to a 32-point afternoon, well above his postseason average of 19.4 ppg. He also dished out eight assists. To counter this on Tuesday, the Suns moved Marion, their second best defender, to Parker. When Parker was suddenly confronted with a rangy and long defender, he was no longer able to get open looks nor could he find passing lanes so readily. Marion’s suffocating defense held Parker to a harmless 13 points on 5–14 shooting. In addition, Parker handed out only three assists and committed four turnovers.

Marion’s work on Parker, one of the Spurs’ key perimeter threats, deserves accolades, but the Matrix contributed inside, too. Another key to the Spurs’ Game 1 win was the team’s huge rebounding advantage, 49–35. The Suns are usually outboarded, but that kind of margin is catastrophic. Marion’s 10 rebounds helped the Suns close the gap on one in Game 2.

Marion’s stellar defense complements the fine play of the Suns’ best defender, Raja Bell, who has reduced the Spurs swingman, Manu Ginobili, to a footnote in the series. Bell’s tenacious defense limited Ginobili, the Spurs’ thirdleading scorer, to only six points on Tuesday after holding him to eight on Sunday.

Although Tim Duncan’s overall numbers were impressive — 29 points on 12–20 shooting and 11 boards — Thomas earned his props by making the Spurs’ superstar work hard for most of his buckets. Several of Duncan’s hoops came on shots that he probably wouldn’t try again even in a free-spirited game of horse. Also, Thomas’s defense freed up Stoudemire for the easier task of keeping Francisco Elson and Fabricio Oberto in check, and enabled the big man to spend more energy on offense. Stoudemire responded with 27 points on 10–16 shooting, and nine boards.

With the Spurs struggling on offense, their defensive attention began to lag as well, and by the middle of the third quarter the Suns were finally getting open looks behind the arc, and the team made its first dunks of the series.

So what does San Antonio do now? The major factor lies in getting more and more consistent offense from the Spurs’ other role players. Guard Michael Finley poured in 19 on Sunday but took only nine shots on Tuesday night; Brent Barry has gone scoreless in 23 minutes, and Robert “Big Shot Bob” Horry should take some of Elson or Oberto’s minutes and draw Stoudemire farther from the hoop by nailing some three-pointers. Any and or all of these measures would help.

The onus remains on the Suns to win at least one of the games in San Antonio, but with the Suns’ win on Tuesday, the team has proved itself capable of doing just that. After losing 12 of 16 to San Antonio, Phoenix finally has an effective blueprint on how to beat the Spurs.

mjohnson@nysun.com