LOS ANGELES — Ninety minutes before the Rams new offense made its preseason debut against the Cowboys, its new top receiver stood in the tunnel of the Coliseum in street clothes. Sammy Watkins was reeling from news of his trade a day earlier. He’d just arrived in Los Angeles from Buffalo, whisked from the airport to the stadium. For Watkins, it was a whirlwind. For the Rams, his arrival was an adrenaline shot for a Rams passing game still in desperate need of one.

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New Rams receiver Sammy Watkins ‘can’t wait’ to get in new offense after trade The payoff would have to wait. Watkins knew little about the Rams offense and nothing about his expected role. He hadn’t met Jared Goff, the quarterback whose career he’s billed to save, or Sean McVay, the coach who plans to turn him into the No. 1 Rams have lacked since Torry Holt. He’d be forgiven, too, if he didn’t know the mustachioed man in the expensive suit, shaking his hand on the sideline, was the team’s owner, Stan Kroenke.

“I just can’t wait to get on the field and figure those guys out,” Watkins reiterated more than once.

But while the Rams’ new No. 1 wideout watched from midfield, it was another new receiver who started his preseason on an especially impressive note.

Since the Rams drafted him in the third round this past April, Cooper Kupp had already surpassed expectations. By the first day of training camp, he’d forced his way to the top of the depth chart at slot receiver, and since camp started, it was Kupp who seemed to be open, day in and day out.

As all eyes focused on Watkins on Saturday, it was Kupp again who separated himself from the pack in a 13-10 preseason victory over the Cowboys.

Sometimes, the separation was literal. After the Rams recovered a muffed punt early in the first quarter, Goff rolled out on a playaction boot and found Kupp wide open in the middle of the field for a 19-yard gain. Two plays later, as Robert Woods fumbled near the goal line, it was Kupp who slipped between two Cowboys and dove for the loose ball, scoring his first-ever NFL touchdown.

“When you dream of your first NFL touchdown, that’s not exactly how you dream it up,” Kupp said, after. “But I’ll take it.”

The Rams will gladly take it, as well. Kupp’s football IQ has already been a hit with McVay, who has consistently raved about his rookie wideout’s development. Kupp’s understanding of coverages and route concepts, McVay has said, is far more advanced than most rookies.

“He’s one of those players that always seems to be in the right spot,” McVay on Saturday. “That’s a credit to his football IQ. He’s going to continue to improve. He’s a very smart, conscientious player. We feel fortunate to have Cooper on our team.”

Before Watkins was added to the picture, the Rams made a concerted effort to revamp their receiving corps during the offseason. They let starters Kenny Britt and Brian Quick walk in free agency. They signed Robert Woods, a sure-handed intermediate receiver, from the Bills. And they put their hope, again, in a breakout season from Tavon Austin, who was expected — or, at least, paid — to be the Rams’ most dynamic wideout.

Austin has so far been the only obstacle in that plan, as he’s spent most of training camp nursing a hamstring injury. Woods, meanwhile, has proven reliable, but has also never been the No. 1 wideout type.

With Watkins set to join practice this week, Kupp may not have the makings of a No. 1, either. If the team has its way, their newly acquired wideout will hold onto that spot for many years to come.

Watkins was the one who fans greeted with a standing ovation during Saturday’s fourth quarter. He’ll be the one fans anoint as their first No. 1 wideout since the days of Holt, Bruce, and the Greatest Show on Turf.

The attention will remain on Watkins going forward, and for good reason. Receivers like him are rarely available. Even Kupp said he “couldn’t wait to get on the field with him.

But as defenses hone in on the Rams’ new home-run threat, it’s the rookie from Eastern Washington who’s determined to slip by unnoticed.

And when he does, he’ll probably be wide open.