Thomas completed 15 of 23 attempts for 196 yards with a touchdown and an interception, which came on the opening series and was returned for a touchdown by true freshman Terrance Mitchell. Costa was 7 of 13 for 104 yards.
Mitchell, one of the stars of spring practices, could end up starting at one cornerback spot.
With running back LaMichael James mostly watching, skilled backup Kenjon Barner had a big day, rushing for 96 yards on nine carries and catching a 20-yard pass. Coach Chip Kelly told reporters than Barner and receiver Jeff Maehl were the "MVPs of the offense" this spring.