In fall practice, before USC's 2007 season, Sanchez broke his right thumb, missing the first game against Idaho; he returned the following week and served as the primary backup to Booty.
Sanchez earned limited playing time in wins against Nebraska and Washington State.
Sanchez was named the starting quarterback by head coach Pete Carroll against Arizona after Booty suffered a broken finger during a 24–23 loss to Stanford.

On October 13, Sanchez led USC to a 20–13 victory, overcoming a wavering performance during the first half of the game in which he threw two interceptions, as Arizona went on to tie the game heading into halftime.
During the second half, Sanchez was more proficient in passing the ball and ultimately finished the game completing 19 of his 31 passes while throwing for 130 yards with one touchdown and two interceptions.
With Booty still recovering, USC elected to start Sanchez for a second consecutive week against Notre Dame; he made significant improvements, completing 21 of his 38 passes for 235 yards and four touchdowns in a 38–0 victory over Notre Dame.

On October 27, Sanchez started for the final time in place of the injured Booty, an away game against Oregon at Autzen Stadium.
USC lost, 24–17; Sanchez had two passes intercepted by Oregon safety Matthew Harper in the second half.
The first interception led to a fourth-quarter touchdown that gave Oregon a 14-point lead; the second interception ended USC's final chance for a comeback.
In spite of a myriad of mistakes committed by his teammates in addition to his own, Sanchez publicly accepted blame for the loss.
The following week, against Oregon State, Booty returned as USC's starting quarterback, with Sanchez resuming his position as Booty's backup.
Sanchez did not perform in subsequent games and finished the season with 695 yards and seven touchdowns with five interceptions.
In fall practice, before USC's 2007 season, Sanchez broke his right thumb, missing the first game against Idaho; he returned the following week and served as the primary backup to Booty. Sanchez earned limited playing time in wins against Nebraska and Washington State. Sanchez was named the starting quarterback by head coach Pete Carroll against Arizona after Booty suffered a broken finger during a 24–23 loss to Stanford.
On October 13, Sanchez led USC to a 20–13 victory, overcoming a wavering performance during the first half of the game in which he threw two interceptions, as Arizona went on to tie the game heading into halftime. During the second half, Sanchez was more proficient in passing the ball and ultimately finished the game completing 19 of his 31 passes while throwing for 130 yards with one touchdown and two interceptions. With Booty still recovering, USC elected to start Sanchez for a second consecutive week against Notre Dame; he made significant improvements, completing 21 of his 38 passes for 235 yards and four touchdowns in a 38–0 victory over Notre Dame.
On October 27, Sanchez started for the final time in place of the injured Booty, an away game against Oregon at Autzen Stadium. USC lost, 24–17; Sanchez had two passes intercepted by Oregon safety Matthew Harper in the second half. The first interception led to a fourth-quarter touchdown that gave Oregon a 14-point lead; the second interception ended USC's final chance for a comeback. In spite of a myriad of mistakes committed by his teammates in addition to his own, Sanchez publicly accepted blame for the loss. The following week, against Oregon State, Booty returned as USC's starting quarterback, with Sanchez resuming his position as Booty's backup. Sanchez did not perform in subsequent games and finished the season with 695 yards and seven touchdowns with five interceptions.
Mark Sanchez