By TERESA M. WALKER
AP Pro Football Writer
NASHVILLE, Tenn. (AP) — The San Francisco 49ers, led by two-time Pro Bowl defensive end Nick Bosa, turned in a mighty defensive performance against Tennessee on first and second down. Third down was another story. The Niners gave up big play after big play Thursday night with a chance to get off the field and blew a 10-0 halftime lead in losing 20-17 to the Tennessee Titans. The 49ers looked dominant on first and second downs, holding the Titans to an average of 3.19 yards per play. The Niners gave up an average of 9 yards a play on third down.