Tramaine Brock 49ers preseasonPay close attention to how 49ers cornerback Tramaine Brock plays in replacement of Tarell Brown next Monday, because he’ll probably be one of the team’s two starting cornerbacks come 2014.

The 49ers agreed to terms on a four-year, $16 million contract extension with Brock today, according to multiple reports. The extension includes $7 million in guaranteed money — the cherry on the cake that seems to have “starter-style contract” written on the icing.

Brock was only a fringe player for the 49ers over the last few years — he signed with the 49ers after going undrafted out of Belhaven College in 2010 and was one of the bubble players during the team’s final roster cuts last season. Injuries to Chris Culliver and Nnamdi Asomugha gave Brock a chance for extending playing time this season, and to say the 25-year-old corner has taken advantage is an understatement. In 10 2013 games, Brock has 18 total tackles, four interceptions (including a pick-six) and nine passes defended. Pro Football Focus has him graded out at a ridiculous +5.9 overall for the season, despite scoring at -1.2 on run defense.

Just as the 49ers have come under some criticism for failing to develop wide receivers, they’ve been exceptional producing playmakers in the defensive backfield. Eric Reid seemed destined to be a star from the beginning, but he’s transitioned flawlessly from college to pros. Dashon Goldson was a mid-round pick that turned into a bank-breaker for the Buccaneers in free agency. Brown was in Brock’s position before stepping up to the plate and delivering over the last three years. The same could be said for Culliver, despite his downfall during last year’s playoffs (on and off the field).

The question is whether Brock’s recent performance is an anomaly or a trend, and the 49ers’ front office seems to believe it’s the latter. We should get a chance to see, not only how Brock performs playing every defensive snap, but also how he does against teams’ No. 1 wide receivers. Brown’s injury will ensure that on Monday night against Washington, and maybe a good deal longer. For better or for worse, Brock will be a staple in this defense for a few years to come.