HOUSTON -- Quarterback Alex Smith was under pressure throughout his 21-play stint Saturday night in the 49ers' exhibition game against the Houston Texans.Smith managed to escape the game without injury. However, the 49ers were not as fortunate with running Brandon Jacobs, who went down in the first quarter with a left knee injury.The extent of Jacobs' injury was not immediately known. Coach Jim Harbaugh and athletic trainer Jeff Ferguson assisted Jacobs off the field. He was then taken from the sideline to the locker room on a cart.With Jacobs unavailable the 49ers gave the ball to Anthony Dixon on two fourth-and-1 situations. He converted one try, but was stopped on the other at the Houston 20-yard line.The Texans led the 49ers 10-6 at halftime, as the Texans' first team put together the half's only touchdown drive against the 49ers' second-stringers.Smith played the first two possessions of the game, completing five of nine passes for 49 yards. He was sacked twice under pressure throughout his 21-play stint.Smith completed a 24-yard pass to Ted Ginn on a deep out to put the 49ers in field-goal range. Running back Frank Gore started, played two snaps and touched the ball once. He tore off a 14-yard run, and was promptly replaced by Kendall Hunter.Randy Moss got his first reception of the exhibition season when he caught a 5-yard pass on the opening drive. Moss had three receptions for 24 yards in the first half.Colin Kaepernick entered the game for the 49ers' third possession and prompted took off on a 12-yard run. The drive stalled after Moss dropped a back-shoulder throw. David Akers kicked a 36-yard field goal.Here's a look at the 49ers' offensive play time in the first half:QB: Alex Smith 21, Colin Kaepernick 8
RB: Frank Gore 4, Kendall Hunter 17, Bruce Miller 10, Anthony Dixon 3, Brandon Jacobs 1, LaMichael James 5.
WR: Michael Crabtree 14, Mario Manningham 13, Randy Moss 14, Ted Ginn 9, Kyle Williams 12, A.J. Jenkins 2, Brett Swain 2.
TE: Vernon Davis 21, Demarcus Dobbs 1, Konrad Reuland 13, Garrett Celek 2.
LT: Joe Staley 27, Mike Person 2.
LG: Mike Iupati 27, Joe Looney 2.
C: Jonathan Goodwin 27, Daniel Kilgore 2.
RG: Alex Boone 27, Leonard Davis 2.
RT: Anthony Davis 27, Kenny Wiggins 2.