Marion, playing on his college's home court at UNLV's Thomas & Mack Arena, was 6-for-10 from the field.
Kobe Bryant was at the game but did not play for the Lakers. Bryant, who is recovering from July 15 knee surgery, practiced with the team Friday and Saturday.
Smush Parker led the Lakers with 18 points, going 5-of-6 from 3-point range. Shammond Williams and Luke Walton each added 12 points for Los Angeles. Lamar Odom, who played 24 minutes, scored nine. Ronny Turiaf had seven points, 10 rebounds and three blocks.
The Lakers were coached by Kurt Rambis. Head coach Phil Jackson will return for the regular season after having hip replacement surgery.
The Suns led through most of the game, except for two minutes early in the second quarter. After leading 52-47 at halftime, Phoenix built its largest lead at 73-59 with 4:28 left in the third quarter.
Phoenix was 22-of-26 (85 percent) from the foul line, while the Lakers were 8-of-14 (57 percent).
The Suns were playing their first preseason game in the United States after playing one game in Italy and two in Germany. Two of those games were against foreign teams, the other was a loss to the Philadelphia 76ers.
The Lakers lost for the first time in the preseason after beating Utah and Seattle last week. This was their first of two games in Las Vegas. They also play Sacramento on Tuesday.