SAN DIEGO -- Want to hear something scary?

At least for opposing defenses.

San Diego Chargers rookie receiver Keenan Allen said there’s still room for improvement after scorching the Indianapolis Colts’ secondary on nine receptions for 107 yards, including a 22-yard reception for a score in his team’s convincing 19-9 win on Monday night.

“I’m still a rookie,” Allen said, smiling. “But yeah, I’m definitely trying to grow and develop as a player. I’m just taking it all day by day and trying to gain confidence.”

With fellow receiver Malcolm Floyd on injured reserve with a season-ending neck injury, Allen has stepped in nicely and earned Philip Rivers' trust.

In just six short games, Allen is developing into a No. 1 receiver for the Chargers, someone who can be counted on to create impact plays on a weekly basis.

“We just have to sustain it now,” Rivers said. “Sustain the confidence, the trust and the consistency. It may be a four-catch week next week, but his play is going to be key -- being there when his number is called.”

Through six games, Allen has made his mark. He’s totaled 23 receptions for 332 yards and two touchdowns. Only DeAndre Hopkins (25) and Tavon Austin (24) have more receptions than Allen among rookie receivers, but both of those players were drafted in the first round.

Allen was considered a first-round talent but tumbled down the draft board because of NFL teams’ concerns about a posterior cruciate ligament injury he suffered during his final season at Cal.

Allen said he uses that as motivation.

“I think so,” he said. “A lot of teams didn’t want to take a chance on me because of my knee. I wasn’t really concerned about my knee, but it happened, so I just try and keep playing ball.”

At 6-foot-2 and 211 pounds, teammates say Allen is faster than he looks. His bigger body helps him create separation against smaller defensive backs. But he also can make defenders miss after the catch, which contributes to his 14.4 yard-per-catch average.

“He’s definitely is deceiving, his speed,” San Diego cornerback Shareece Wright said. “And he has more short-area quickness -- getting off the line he’s really quick. He’s not a heavy dude; he’s like a long, not heavy, but not skinny guy.”

So what other receiver does Allen compare to?

“He’s really unique,” Wright said. “He has that long torso like a track athlete. He’s not a Malcom Floyd. He’s not a Vincent Brown. He’s not a Danario Alexander. He’s just kind of his own dude. He’s Keenan Allen.”

Rivers said Allen’s 22-yard touchdown was another confidence-building catch-and-throw between the young receiver and a veteran quarterback. Allen wasn’t the primary read on the play, but Rivers saw a way to get the ball to Allen in the back of the end zone, and, fortunately, Allen saw the same thing.

“The safety, he drove on Gates and got too far down the field, and Philip threw it over his head, and he couldn’t come back to it, and I just tried to run up under it,” Allen said.

Said Rivers: “Those are the kind of trust-building plays that you have to make. You don’t make that play until you make that play. That doesn’t come up like that ever in practice. So you don’t really know until you throw it -- 'Is he thinking what I’m thinking?' And then when you make it, you’re like, ‘All right, check mark on that.’ You build confidence that way, by making plays in games like you did today.”

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