ORCHARD PARK, N.Y. -- Buffalo Bills quarterback Josh Allen completed 18 of 33 passes for 245 yards, one touchdown and two interceptions while making his NFL starting debut in a 31-20 loss Sunday to the Los Angeles Chargers.

Allen, whom the Bills traded up to select with the No. 7 overall pick in April's draft, was sacked five times and finished with a 63.3 passer rating. He also ran eight times for 32 yards.

"I felt comfortable for the most part," Allen said after the game. "There's some things that [Los Angeles] did that we didn't see on film, and I didn't see on film. But that's being a rookie. That's the part of it. A defensive coordinator is always going to try to throw you something different and get you out of your element, and I have to do better with the pass protection. I have to be better with getting the ball out quicker."

The Bills begin the season 0-2 for the first time since 2016. They have been outscored 78-23 over their first two games. Running back LeSean McCoy did not finish Sunday's game because of a rib injury. McCoy was hurt on a 1-yard run in the third quarter in which center Ryan Groy fell on McCoy's midsection as he was being tackled. McCoy returned to take another carry on the final play of the third quarter but did not carry the ball in the fourth quarter.

McCoy, who was in obvious pain while walking around the locker room and while changing clothes, declined an interview request after the game because he was having difficulty speaking.

McCoy finished the game with 39 yards on nine carries, as well as four catches for 29 yards.

Allen completed a 57-yard pass to wide receiver Zay Jones late in the second quarter. According to NFL Next Gen Stats, the pass had 64.0 of air distance from the spot of the throw to the spot of the catch. That is tied for the second-longest air distance on a completed pass since 2016, when NFL Next Gen Stats began tracking.

"I thought overall, offensively, we got off to a slow start," Bills coach Sean McDermott said. "Having said that, there were some moments that I thought were pretty solid and then some moments that I know Josh would want back."

Allen led the Bills on a seven-play, 75-yard drive ending in a 1-yard touchdown run by Chris Ivory to begin the second half, but he was intercepted later in the third quarter by Chargers safety Adrian Phillips on a throw Allen made while being wrapped up for a would-be sack. Allen was intercepted again in the fourth quarter by Chargers linebacker Kyzir White when he underthrew tight end Jason Croom.

"[The] two interceptions, they were just two plays that I could've changed," Allen said. "The one that I was trying to throw to [running back Marcus Murphy], I was held up and I should've just taken a sack or thrown it away. The one to [Croom], he was running over the top, and I just made a bad ball. I should've allowed him to run under it, but I put it out in front of him and didn't put enough air on it. That was all my bad."

With the Bills trailing 31-13 late in the fourth quarter, Allen completed a 12-play, 75-yard drive with a 3-yard touchdown pass to Kelvin Benjamin.

Allen's passer rating was the worst mark in a starting debut among the four quarterbacks the Bills have drafted in the first round during the common draft era. Jim Kelly, who was a first-round pick in 1983, had a 119.8 rating in his 1986 debut for Buffalo after a stint in the USFL. J.P. Losman (first round, 2004) posted an 89.9 rating in his 2005 debut, and EJ Manuel (first round, 2013) compiled a 105.5 rating in his first start as a rookie.