PHOENIX (AP) – Facing perhaps the biggest game thus far in their storybook season, the Phoenix Suns believe the only significant change necessary must come in their hearts and their heads.

“Attitude is the No. 1 thing,” coach Mike D’Antoni said. “It’s human nature to rest on your laurels. We have to fight that. If you want to be a champion, there’s no time to think “Oh good, look what we did.’ That crept in a little bit in Game 4.

“That won’t happen in Game 5. That I can guarantee. I can’t guarantee a win. I don’t know how anybody does that. But I can guarantee we’ll be ready to roll.”

Dallas’ 119-109 victory in Game 4 on Sunday tied the best-of-seven Western Conference semifinal series at 2-2. Game 5 is tonight, and the winner in these situations usually goes on to take the series. A Suns loss would put the team that won an NBA-best 62 regular-season games on the brink of elimination.

The high-scoring showdown arguably has been the most entertaining of all the semifinal series, and both teams believe they need to play much better in Game 5.

“I’m convinced there’s another level for us to go,” Mavericks coach Avery Johnson said.

“We’re playing a terrific team. We can’t make as many mistakes as we’ve been making.”

In the Game 4 victory, Dallas sent two or three defenders at Amare Stoudemire, and dared Steve Nash to do the scoring. Stoudemire managed only 15 points, the first time he’s been held under 30 in seven games against Dallas this season. Nash, meanwhile, had a career-playoff-high 48 on 20-for-28 shooting.

The Suns expect similar defensive tactics in Game 5.

“I’m willing to keep scoring. That’s no problem,” Nash said. “Like I said, the offense wasn’t the problem in that game. It was a winnable game, we just didn’t play hard enough. That’s why we lost.”

The Mavericks weren’t expecting 48 points from the league’s MVP, but they feel their approach is the best available against a team that averaged 110.4 points in the regular season and 114.5 so far in the playoffs.

“We have to take him out of his comfort zone, get him doing things he doesn’t like doing,” Mavs guard Jason Terry said.

x “His comfort zone is to break down the defense, get in the lane, hit Amare and let him dunk, break down the “D,’ kick it out for three. But scoring bucket after bucket, that’s not where he’s most comfortable.”

Stoudemire believes he can be a force even with the Mavs sending multiple defenders at him.

“There ain’t no question about it,” he said. “I feel I can still get big numbers, just by my raw talent.”

D’Antoni and Nash agree that the Suns lost Game 4 because of a lethargic start.

“In the first half, we were really complacent,” Nash said. “We felt like this was going to be easy, and it’s just not that way. They’re too good a team for us to lay down for a quarter and a half in the playoffs. They won 58 games for a reason.”

Neither team will be mistaken for a defensive powerhouse. But the Suns took defense to a new low in the first half of Game 4, when they fell behind by 21 points.

“Everybody says, and it’s true, that you have to win on your defense,” D’Antoni said. “But our defense means hold them under 110, it doesn’t mean keep them in the 80s. We didn’t do what we were supposed to do.”

Dallas will not have Keith Van Horn in uniform. Van Horn, sidelined the entire series with a sprained left ankle, practiced on Tuesday but Johnson said he was “not physically available” for Game 5.

Expect another iron man performance by the Suns starters. Joe Johnson, who fractured his left eye socket in Game 2, watched practice on Tuesday but is a long way from being ready to play again. With almost no help from the bench, the five Phoenix starters know they will have to play nearly all the game.

The Mavericks have talked about how their depth could be a deciding factor if the series goes long.

D’Antoni scoffs at that idea.

“They’re not going to wear us down,” he said. “That’s not going to happen. Now they might beat us, but they’re not going to wear us down.”

AP-ES-05-17-05 1959EDT