By Dan Durkin-

(CBS) While it may not have come under the most ideal of circumstances, Bears rookie cornerback Kyle Fuller made the most of his expanded role last Sunday in a win against the 49ers.

In the third quarter, veteran cornerback Charles Tillman was lost for the rest of the game and, we’d find out, the rest of the season with a ruptured triceps. Previously, Fuller had been playing outside only when the Bears were in nickel, but the injury to Tillman thrust him into a featured role, and the rookie rose to the occasion. Fuller intercepted Colin Kaepernick twice in the fourth quarter, setting the offense up with short fields, which Jay Cutler and Co. converted into two touchdowns in their thrilling 28-20 comeback victory.

On his first interception, Fuller made a great break on the ball, played Michael Crabtree’s up-field shoulder and knifed the ball loose. Then it was Fuller’s second interception that really showed this rookie is savvy beyond his years and playing experience.

Let’s go to the film room to take a closer look at the second pick, while also reliving the play through Fuller’s eyes and mind.

With 9:19 remaining in the game, the 49ers had the ball on third-and-12 at their own 35-yard line and broke the huddle in 11 personnel lined up in a doubles formation. The Bears responded with their nickel personnel in a two-high look.

After the snap, the Bears rotated from their two-deep look into a single-high safety look.

Click to enlarge the photos. All images courtesy of NFL Game Rewind.

1

“Three-deep coverage, I had two guys, verticals on my side,” Fuller said of what he saw.

Reading safety Ryan Mundy dropping to his landmark, Kapernick read Fuller’s side of the field the entire play.

2

Fuller carried Crabtree on the vertical route, but at the top of his route stem, Crabtree snapped off his route on a comeback.

“Going off my field one (No. 1 receiver on his side – Crabtree), he broke it down, but I also still felt the tight end going up the seam and also the quarterback looking,” Fuller said.

3

Jared Allen’s rush forced Kaepernick to step up in the pocket, and Will Sutton’s rush forced Kaepernick to step laterally to his left. Looking back at Kaepernick, tight end Derek Carrier stemmed his vertical route to the sidelines, where Fuller has dropped into his deep-third responsibility up the sidelines.

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Kaepernick tried to thread the ball to Carrier, but Fuller read his eyes and undercut the route for the interception.

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This play demonstrated Fuller’s football smarts to quickly read his keys as well as his athletic burst to quickly change direction, drive on the ball and make a play.

“I was able to come off of one (Crabtree) and make a play,” Fuller said. “It really comes down to using my technique and fundamentals. The coaches, you know, we talk about it all the time — if one sits down, you still have to take care of two (Carrier) going vertical. So, I was just doing what I was taught and what I’m working on every day.”

It was only one game, but an impressive one at that for the Bears’ first-round draft pick. It’s been a while since a Chicago rookie has stepped in and made impact plays early on, so this is an encouraging start to Fuller’s career.

Fuller is savoring the moment while keeping the right mindset moving forward.

“I’m definitely trying to enjoy that (two interceptions), but at the same time, I’m trying to get my mind ready for next week,” Fuller said.

Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.