Mathis is the backup for J.P. Arencibia and typically has started once in a series that includes a day and night game, but this time manager John Farrell opted to go with the matchups.
Farrell wanted to give Mathis a start with powerful right-hander Ervin Santana on the hill for Los Angeles.
"I like Jeff against guys with high velocity," Farrell said. "That's not to say J.P. can't hit those types, but knowing we were going to pick a spot for him in this series, this is where tonight was the matchup."
Mathis is a career .195 hitter but has enjoyed a strong start to the season. He has opened up his batting stance, and the change in mechanics has led to a .294 average with four extra-base hits in just 17 at-bats.
The 29-year-old was acquired from the Angels during the offseason for left-hander Brad Mills.