Cotton Fitzsimmons, the Phoenix Suns' coach, was as perplexed as anyone. They had thrown up air balls and bricks for four quarters and been blown out by a record 39 points by the Jazz in the NBA's first-round playoff game. They ended up shooting a weak 40.5 percent from the field and only 62.5 from the free throw line.

For a team that has built a reputation on fine shooting, Thursday night's 129-90 playoff loss to the Jazz was something put under a microscope.But there were no high-level explanations forthcoming.

"It's just one of those games," said Fitzsimmons. "I really have no explanation on why our team looked so poorly. The Jazz just did a great job."

As simple as it may sound, Fitzsimmons' answer was as good as anyone could produce. In playing one of their finest defensive games of the year, the Jazz helped dictate the course of events. In the first 51/2 minutes they forced five turnovers. Meanwhile, they also hit a spectacular 65 percent from the field for the game.

"I don't think we've played a full game this well all season," said the Jazz's Jeff Malone.

He continued, "We put a lot of pressure on them. You've got to give us credit. Our defense had a lot to do with it."

But for all their defensive intensity, the Jazz couldn't have won by that margin without help. They got it in Phoenix's horrible shooting. The Suns missed numerous open shots, bungled defensive assignments and generally looked like a crew on shore leave.

"I think that we played excited," said guard Kevin Johnson, "but we didn't hustle and there is no excuse for that. This is not our first year in the playoffs."

Nor is it their first playoff against the Jazz. The teams have met twice under similar conditions, with Phoenix eliminating the Jazz 4-2 in 1984 in the Western Conference semifinals in 1984, and 3-2 last year. Overall, the Suns are 7-5 in playoffs against the Jazz, 4-2 in Phoenix.

Despite Thursday's loss being a record playoff margin for the Suns, it may not have been their worst showing. In 1970 Phoenix made only 36 of 111 shots (.324) in a game at Los Angeles.

"They missed a lot of shots," said Jazz Coach Jerry Sloan."Every other time we've played them, when they shoot, you're sitting on the edge of your seat."

He continued, "It's hard to imagine them shooting the ball as poorly as they did. They usually just kill us."

Meanwhile, the Jazz say they are taking no comfort in what has now become their home-court advantage. (The teams meet in Phoenix on Saturday, then next Tuesday and Thursday in Salt Lake.) Winning by 39 does not necessarily a series make. "We can lose by 50, too," said Sloan.

"This is just one game," the coach continued. "They're certainly not out of it. That's one thing about basketball - you never know what's going to happen. There's still a lot of basketball to be played still. We know who Phoenix is."