SANTA CLARA -- Tramaine Brock's aggressive style and football instincts were on bright display even before he deflected a pass to NaVorro Bowman for Monday night's win-clinching interception return.

Two snaps earlier, Brock body slammed Harry Douglas into Candlestick Park's 7-yard line after a 9-yard catch.

"I felt I could slam him, so I just slammed him," Brock said.

Brock figured his anger stemmed from Douglas catching a couple of slant passes on him earlier in the 34-24 win. What mattered most in the end is that Brock cut off one final slant route by Douglas, the one that resulted in Bowman's 89-yard interception return for a touchdown with 1:10 remaining.

San Francisco 49ers’ Tramaine Brock breaks up a pass against Atlanta Falcons’ Harry Douglas (83), leading to 49ers’ Navarro
San Francisco 49ers' Tramaine Brock breaks up a pass against Atlanta Falcons' Harry Douglas (83), leading to 49ers' Navarro Bowman's touchdown on an interception at Candlestick Park in San Francisco, Calif. on Monday, Dec. 23, 2013. (Nhat V. Meyer/Bay Area News Group)

"I go out and play aggressive. That's the way I always played in college at high school," said Brock, a product of Mississippi's Belhaven University and Long Beach High. "I'm trying to follow it up now. It's just how I play. I don't know where it comes from."

Brock came into this season's defensive picture once he replaced Nnamdi Asomugha as the nickel back after three games. When Tarell Brown sustained a rib injury on a touchdown-saving tackle at New Orleans on Nov. 23, Brock took over as the right cornerback.

Matt Ryan's final pass Monday night resulted in Brock's team-high fifth interception this season. Of those five, his first was his best: he returned it 18 yards for a touchdown on the third play of an Oct. 6 win over the Houston Texans.

"He's always been a fairly physical player and done well here on special teams when he wasn't playing defense," 49ers defensive coordinator Vic Fangio said. "And like I said before, we always felt he had the ability. He just needed an opportunity, and he needed to show it when he got his opportunity. And he's done that."

Brock indeed has shown his feisty side over the years as a special-teams gunner, to which he said: "Special teams is something I had to do to get where I am now."

Come Sunday's regular-season finale, he'll renew one of his first career matchups, that against Arizona Cardinals star Larry Fitzgerald. Brock recalled how they met in the 2010 regular-season finale and "it didn't go that well for me." Fitzgerald had 11 catches for 125 yards and a touchdown while the 49ers still won 38-7.

The following year, Brock was poised to be the 49ers' nickel back, but a hand injury sidelined him and allowed Chris Culliver to take that spot for the 2011 and 2012 seasons. When Culliver went down with a knee injury in training camp, that set in motion Brock's return up the depth chart.

"I just kept competing through training camp and that led me to here," said Brock, who got rewarded last month with a four-year, $16 million contract extension.

Said safety Donte Whitner: "He's a guy that wants to be physical. He's not the biggest guy. He wants to get his hands on the football. He wants to be a playmaker. He wants to be physical and everybody feeds off of that, also. So he's been playing great."

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