The San Diego Chargers and Baltimore Ravens are each on the verge of a fourth straight loss, which would go a long way in sinking either's hopes for a playoff spot.

Both are relying heavily on their quarterbacks because of abysmal defenses, making Sunday's meeting in Baltimore a potential shootout.

Philip Rivers and Joe Flacco, along with the New York Giants' Eli Manning, are the league's only signal-callers to start each game for their current team since the beginning of 2008. Both have shouldered large workloads this year, with Rivers attempting 209 passes over his last four games - the most by a Super Bowl-era quarterback in a four-game span.

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He leads the NFL with 2,452 passing yards, putting him on pace for an NFL-record 5,604. The current record is Peyton Manning's 5,477 for Denver in 2013.

The Chargers (2-5) fell behind Oakland 30-6 in the first half of last Sunday's 37-29 loss, dropping three in a row for the first time since a four-game slide in 2012. They've lost eight of 11 dating to last season and are tied with Kansas City for last place in the AFC West.

"We got outplayed and outcoached in the first half," coach Mike McCoy said. "It's very difficult to have success when you start the game like we did, whether it's turnovers or giving up seven straight scores. That starts with me as the head coach. We're not going to sit around and dwell on this."

It's going to be difficult for San Diego to make up ground without improving on defense. The Chargers are allowing 28.3 points per game to rank 27th, and their 6.5 yards per play given up are the most.

Baltimore (1-6) has put a big burden on Flacco because of poor defense, too, ranking 26th with 26.9 points allowed. Flacco's 1,857 passing yards are the third-most by a Ravens quarterback through the club's first seven games, and he ranks fourth with 41.0 attempts per game.

The Ravens came up short again Monday in Arizona, losing 26-18. Each of Baltimore's defeats have come by eight points or fewer, and its start is a far cry from what was expected with many pegging it as a trendy Super Bowl pick.

"A lot of teams would fold in this situation, but not the Ravens. That's not going to happen," coach John Harbaugh told the team's official website. "We will be writing the story, and it's going to be a really interesting story to read before it's all said and done."

After being an institution in the NFL for more than a decade, the Ravens' defense looks like anything but that. Baltimore gave up 414 yards to Arizona, already the fourth time it has surrendered at least 400 - an amount the team allowed only five times over the previous two seasons.

The Ravens rank 26th allowing 5.9 yards per play after finishing 10th or better 15 of the last 16 years, including 10 top-five finishes. They gave up 5.2 a season ago.

They've also been faced with an arduous schedule that put them on the road for five games already, including three in the Pacific time zone.

Baltimore's next three games are at home against opponents that are a combined 7-13, and November is typically when the club has thrived under Harbaugh, going 12-2 at home for the NFL's best mark since 2008.

The Ravens haven't dropped four in a row since a nine-game losing streak Oct. 21-Dec. 23, 2007.

"Oh, man, it's amazing," defensive tackle Brandon Williams said of playing at home. "We're definitely excited just to be at home, in our atmosphere, loud fans, crazy crowd and just getting after it, playing Raven football."

Receivers on both sides have benefited from these pass-happy offenses. San Diego's Keenan Allen leads the league with 62 receptions, while Baltimore's Steve Smith Sr. ranks fourth with 98.0 receiving yards per game despite being the league's oldest wide receiver at 36.

Rivers has averaged 329.3 passing yards in his last four meetings and found Eddie Royal on a one-yard TD pass with 38 seconds left for a 34-33 road win last season, evening the all-time series at five wins apiece.