Coming off their divisional home win over the Raiders, the Chargers flew to Giants Stadium for a Week 9 interconference duel with the New York Giants in the much-hyped first-ever meeting between quarterbacks Philip Rivers & Eli Manning (Drew Brees started for the Chargers when the teams met in 2005). After a scoreless first quarter, San Diego would deliver the opening strike of the second quarter as Rivers completed a 10-yard touchdown pass to wide receiver Vincent Jackson.  The Giants would answer with Manning completing a 6-yard touchdown pass to wide receiver Steve Smith.  In the third quarter, the Chargers regained the lead as Rivers found tight end Kris Wilson on a 1-yard touchdown pass.  New York would take the lead in the fourth quarter as kicker Lawrence Tynes nailed a 38-yard field goal, Manning hooked up with tight end Kevin Boss on an 8-yard touchdown pass, and Tynes booted a 22-yard field goal. San Diego came right back as Rivers threw the game-winning 18-yard touchdown pass to Jackson. With the win, the Chargers improved to 5-3 and kept their winning streak going by 3 games.
Question: How many yards was the longest touchdown pass by Rivers?
Answer: 18