During training camp, Tramaine Brock lost his job as the No. 3 cornerback to Nnamdi Asomugha. It'll be more difficult to pry it away this time.
Brock returned an interception for a touchdown 90 seconds into the game, then nearly did the same in the second quarter. He was pulled down from behind by intended receiver Andre Johnson instead, but the 49ers offense needed only four more plays - including a two-yard touchdown run by Anthony Dixon - to convert that turnover into points.
They lead the Texans 21-0 at the half.
On the third play of the game, Houston quarterback Matt Schaub tried to throw to Johnson, who was coming out of the slot. However, he didn't see Brock, who had been lined up outside, come off his man and run toward Johnson.
Brock broke in front of the receiver, collected the ball and ran into the end zone for an 18-yard touchdown. It was the fourth straight game Schaub had thrown an interception that was returned for a touchdown.
Brock began the offseason as the 49ers' third cornerback, a position that sees plenty of playing time, especially against teams like the Texans that use three or more receivers or treat their tight ends as wideouts. A minor injury to Brock in training camp allowed Asomugha to step into the role, which he kept until suffering a knee injury Sept. 22 against the Colts. Brock added to his solid half by drawing an offensive pass-interference call against receiver DeAndre Hopkins on a deep ball late in the period.
Brock is scheduled to be an unrestricted free agent in March, one of several cornerbacks the 49ers must evaluate between now and the start of the free agency period. Asomugha, Tarell Brown and Eric Wright also are scheduled to be unrestricted free agents. Perrish Cox will be a restricted free agent while Carlos Rogers will count more than any other player against the salary cap.
The 49ers did its part as well.
San Francisco entered the game with a sputtering offense, one that ranked among the league leaders in three-and-out drives. Colin Kaepernick, however, converted three third downs on the team's opening drive, hitting Vernon Davis for 13 yards, Anquan Boldin for 12 yards and Boldin again for nine yards to get to the Houston 1-yard line.
There, the 49ers sent into their "heavy jumbo" run package, and Frank Gore pounded the ball into the end zone over the left side. Gore, who has rushed nine times for 45 yards, seemed to injure his left knee on his last carry. He was replaced by Kendall Hunter on the next 49ers drive.
-- Matt Barrows