The Raiders travelled to face the San Diego Chargers with a chance to secure their first playoff bid since 2002. In a stadium at least half full of Raider fans, the Chargers took an early lead on a pass from Philip Rivers to Travis Benjamin to put the Chargers up 7-0. The Raiders responded with an 11-play drive that stalled on the Charger 27-yard line and had to settle for a Sebastian Janikowski field goal to narrow the lead to 7-3. Neither team could muster anything offensively for the remainder of the quarter. A promising Raider drive to the Charger 16-yard line stalled again as Derek Carr was intercepted inside the 10-yard line. A Charger field goal following a 14-play drive put the Chargers up 10-3 with 1:33 left in the half. The Raider offense switched to their two-minute offense and cruised down the field before Carr hit Michael Crabtree in the corner of the end zone to tie the game at 10. The Raider offense drove deep into San Diego territory to open the second half, but had to settle for another Janikowski field goal to take the lead 13-10. The Chargers answered with a Rivers seven-yard touchdown pass to Hunter Henry to retake the lead. A missed extra point left the lead at 16-13. The remainder of the third quarter saw the offenses accomplish little before Charger running back Kenneth Farrow fumbled at the San Diego 14 early in the fourth quarter. The Raiders offense could not take advantage of the turnover and settled for Jankowski's third field of the game to tie it at 16.  The Raider defense again stopped the Chargers and the offense, lead by Latavius Murray and Jalen Richard, moved the ball into San Diego territory again. For the fourth time, the offense settled for a Janikowski field goal to take the lead 19-16 with 3:47 remaining. On the ensuing San Diego possession, Rivers was intercepted by Reggie Nelson to allow the Raiders to take over and run out the clock. The win gave the Raiders their first playoff appearance since 2002. With a loss earlier in the day by Kansas City, the Raiders also took back first place in the AFC West.
Question: How many points were the Chargers ahead by at the end of the first quarter?
Answer: 4