It was up to the Raven defense to deliver a victory. As usual, Ray Lewis and company made it happen.
The Ravens took a 13-10 lead into the fourth quarter, then converted Leftwich's two fumbles into 10 points before Lewis secured the win by intercepting a tipped pass with 44 seconds left.
"When you play a team like we played today, you have to find a way to get your hands on the football," Lewis said. "We did exactly what we needed to do to come out and win."
The Jaguars (1-7) held the NFL's leading rusher in check and limited the Ravens (5-3) to nine first downs.
Jamal Lewis had 68 yards in 21 carries, ending his streak of 100-yard games at six. Lewis did surpass 1,000 yards (1,045) by the halfway mark of the season.
"It all starts with stopping No. 31," first-year Coach Jack Del Rio, who spent three years as linebackers coach of the Ravens, said of Jamal Lewis. "We had to have that to have a chance. That was the No. 1 goal. Without doing that, we have no chance to beat this football team."
Stacking eight players near the line of scrimmage on almost every play, Jacksonville put the clamps on the league's top-ranked ground attack.
Leftwich completed 22 of 34 passes for 208 yards, including a five-yard touchdown pass to David Allen with 3 minutes 11 seconds to go.
Then, after a Baltimore punt, he took the Jaguars to the Baltimore 29 in the final minute before Ray Lewis clinched the victory, keeping the Ravens atop the AFC North.
Boller finished 10 for 23 for 156 yards. He lost a fumble to set up a Jacksonville touchdown, and had a pass intercepted.