Then he ran out of gas.
The first seven minutes of Marion's tenure with the Mavericks were spectacular. He hit his first three shots and was active defensively as Dallas jumped out to a six-point lead over the Washington Wizards.
Marion didn't make much more noise until garbage time of the Mavericks' 102-91 loss Tuesday night at the American Airlines Center.
"It's a rhythm game," Marion said. "I got out of rhythm a little bit. My legs got a little heavier."
His statistical line (16 points on 6-of-12 shooting, 7 rebounds, 3 blocks and a steal) was fine. But Marion didn't make the Mavericks better most of his time on the floor. After his strong initial seven minutes, the Mavericks were outscored by 21 with Marion on the court.
The Mavericks made a sign-and-trade deal for the 31-year-old Marion, committing $40 million over five seasons, because they thought his athleticism and versatility made him a perfect complement to the team's core. Unfortunately, he spent most of the preseason nursing a strained right calf instead of working with his new teammates.
It might take some time before the Mavs, who won't have fellow former All-Star swingman Josh Howard for another two weeks or so, get the real Matrix.
"We can't put that type of pressure on him in Game 1," Mavs point guard Jason Kidd said. "He's still working his conditioning in and getting a feel for everybody. To put him on that level of expecting big things out of the gate, that's putting too much pressure."
Marion didn't play much during the preseason -- four halves over three games -- but he was splendid in his limited exhibition time. He shot a ridiculous 77 percent from the floor, making it seem like his transition to the up-tempo Mavs would be easy.
Yet he used the words "stagnant" and "confused" to describe his first game that mattered as a member of the Mavericks. The huffing and puffing didn't help Marion, who managed to air-ball a 3-pointer and come up short on a dunk during his scoreless third quarter.
"He plays at such a high capacity," coach Rick Carlisle said. "He's such a great athlete, and when he runs and does everything at such full bore, he gets winded quickly. If he's not in his best shape, the game's going to be a little tougher for him. There's going to be a period here where he's got to get himself in shape. But, look, he's obviously a terrific player."
Marion reported to training camp in magnificent shape. But it's impossible for a player to maintain his conditioning when his leg won't let him run. Marion's workouts were limited to the treadmill and exercise bike for most of the past few weeks.
"That ain't nothin' really," Marion said of the stationary work. "That's not the same."
Unless Marion can reach and maintain his peak form, the Mavericks will have a tough time moving forward in the Western Conference.
Tim MacMahon covers the Mavericks for ESPNDallas.com. E-mail him at firstname.lastname@example.org.