LOS ANGELES – The age-old adage is that it's unwise to overreact to a preseason performance. Following the show that Dak Prescott put on at the L.A. Coliseum on Saturday night, that's going to be easier said than done.

Of course, it was just half of one game – a preseason opener in which both the Cowboys and Rams sat several key members of their teams. But it was hard not to be impressed by Prescott, who, playing in his first preseason game, guided the Cowboys' first-team offense up and down the field with ease.

"I thought Dak did a good job. He had poise and composure," said Cowboys coach Jason Garrett. "He ran the offense well. I thought he managed the game well and executed plays. He made some little plays and also made some big plays."

Starting in place of Tony Romo, Prescott completed 10-of-12 passes for 139 yards, compiling a quarterback rating of 154.5 in the process. If not for two drops by second-year tight end Geoff Swaim, he would have finished his debut with a perfect rating of 158.3

"It was no different than practice," Prescott said. "That's what the linemen were telling me in the huddle -- it's just another day of practice. I just went out there with a clear mind and had fun."

"Fun" is a great way to describe Prescott's four possessions before taking the bench at halftime. It's up for debate which was the most impressive. The first snaps of his career led the Cowboys on a 11-play, 80-yard drive, highlighted by completions of 15, 18 and 12 – and culminating with a vintage, 10-yard touchdown pass to Dez Bryant.

He also led the Cowboys on a six-play, 75-yard drive that concluded with a jaw-dropping deep ball to Terrance Williams for a 32-yard score.

In considering the type of night Prescott put together, perhaps no one offered up better praise than Bryant – who finished with two catches for 28 yards from his young quarterback.

"I think the best thing about Dak is that he is extremely calm. It's like he's been here before," Bryant said. "He's not playing like a rookie. He is going to be very good -- he's special."

The rookie's poise was on full display in his final possession of the night. It was easily the Cowboys' sloppiest of the first half, marred by three offensive penalties and a sack. But facing a 3rd-and-26 from the Rams' 40-yard line, Prescott scrambled 14 yards to set Dan Bailey up for a 44-yard field goal and a 24-7 lead.

"I surprisingly wasn't nervous," Prescott said. "I didn't know if that was bad or not, me not being nervous, but when you have great players around you, and you get to go out there with the ones, it makes the game a little easier."

None of this is to say Prescott should expect to climb the depth chart any time soon. The Cowboys have made it a habit to sit Romo for the preseason opener in recent years, and it's a good bet that the 14-year veteran will see his playing time increase as the preseason progresses.

For the time being, though, the Cowboys have to be encouraged by the first impression of their rookie quarterback. With three weeks remaining in training camp, it will be interesting to see how Prescott affects the conversation about the Cowboys' backup situation moving forward.

"Dak was delivering the ball to everyone," Bryant said. "With him playing behind a great leader like Romo, he is going to learn a lot. He is doing outstanding."