The Ravens have played 9+ quarters of playoff football in 2 weeks. Their key defensive players are old, and will have to keep pace with a frequently up-tempo Patriots offense, which has played 4 quarters in 2 weeks. At some point attrition must take its toll.
Joe Flacco is Baltimore's quarterback. He's hit or miss, sometimes great, sometimes completely ineffective. The Ravens are good enough to win without him (See the aforementioned 2009 playoff game against New England), but after two great playoff performances, he's overdue to crap the bed.
The Patriots have a much better secondary than in their Week 3 loss to Baltimore. Flacco threw for 382 in that 31-30 Ravens win. That was when Devin McCourty was a cornerback, not a safety. Aqib Talib was a Tampa Bay Buccaneer. And Alfonzo Dennard was out with a hamstring injury. Baltimore had 10 pass plays of 20+ yards in that game, 4 of 30+ yards, and 2 40+ yarders. Not to mention a 27 yard pass interference penalty on McCourty.
Now, with Talib and Dennard as the corners, and McCourty as a safety, things are much better. The defense keeps the play in front of them. They tackle well. Talib can play man coverage. Which is more likely, Flacco throwing for 380 yards? Or being intercepted by McCourty?
I'm not being a Dan Shauhgnessy and guaranteeing a steamroll victory. I actually think the game will be close until the 4th quarter. And the Patriots can certainly lose. They can fumble the ball, miss tackles, get confused on coverage, and make enough mistakes to allow Baltimore to win.
But if the Patriots play at or near their best, then how can Baltimore win? How can Joe Flacco and a tired defense prevail? It seems impossible.