In years past, the Ravens depended on their defense to squash the opposition, leaving the offense to do little else but avoid giving the ball away. Now that McNair is at quarterback, late-game heroics are becoming the standard.
One week earlier, McNair struggled before engineering a late drive that produced a field goal and a 15-14 win over Cleveland. He did little against the Chargers (2-1), either, until it mattered most.
"There was no doubt in my mind we would win this game when No. 9 went out there," said Ravens cornerback Samari Rolle, who played with McNair in Tennessee. "He's been through everything you can be through as a quarterback. He's been MVP. He's been in the Super Bowl. He's just got it."
Showing precisely why they obtained him in an offseason trade with the Titans, McNair went 4-for-5 for 43 yards and ran once for 12 yards during the final drive, which began after San Diego intentionally took a safety with 3:12 to go.
"The defense gave us the opportunity by keeping it within six points," McNair said. "We knew if they gave us the opportunity, we have the confidence in ourselves to get the job done."
McNair never faced a third down during the march. After a 17-yard pass to Mark Clayton got the ball to the San Diego 35, McNair ran to the 23 and completed a 13-yarder to Clayton.
On second down, McNair found Heap for the game-winner, leaving the Ravens at 4-0 for the first time.
"If we don't make enough plays to win early, we can make plays to win the game late," linebacker Ray Lewis said. "That's why we brought him here."
The Ravens never led until Heap bulled his way over the goal line with linebacker Shawne Merriman in tow.
"It came down to a missed tackle. I really tried to take his head off," Merriman said.
McNair finished 17-for-30 for 158 yards and two interceptions. He also threw two touchdown passes.
LaDainian Tomlinson ran for 98 yards on 27 carries for the Chargers, who got a touchdown on their first possession and never reached the end zone after that.
"This one hurts because of the control we had the whole game and we let it slip," said quarterback Phillip Rivers, who went 13-for-22 for 145 yards and an interception that led to a Baltimore touchdown.
Rivers accepted blame for a spotty showing by the San Diego offense, which totaled 67 points in wins over Oakland and Tennessee.
"I didn't play as well as I need to for us to win," he said.
For 59 minutes, it appeared San Diego would win on the strength of a defense that yielded only one touchdown in its first two games.
"You got to learn how to finish it off," Merriman said.
The game appeared to turn on a fumble by Baltimore tight end Daniel Wilcox at the San Diego 1 with 5:18 left in the third quarter and San Diego up 13-7. Wilcox took a shovel pass from McNair and lost the ball after being hit by Stephen Cooper.
The play was particularly damaging to the Ravens because coach Brian Billick lost the team's final timeout with an unsuccessful replay challenge.
After a punt, Ravens wide receiver Derrick Mason slipped behind the coverage down the left sideline, but he inexplicably dropped a long throw from McNair that almost certainly would have produced the go-ahead touchdown.
Minutes later, McNair threw his second interception to end a promising drive.
The Ravens closed to 13-9 when punter Mike Scifres intentionally ran out of the end zone. Baltimore took over at its 40, and McNair went to work.
San Diego led 13-7 at halftime after limiting the Ravens to 45 yards on 24 plays.
The Chargers took the opening kickoff and moved 69 yards in nine plays, going up 7-0 on a 31-yard pass from Phillip Rivers to Malcom Floyd. Rivers went 4-for-5 for 60 yards, including a 13-yarder to Antonio Gates on a third-and-13.
San Diego's next possession ended with an interception by Bart Scott, whose 24-yard return set up a 5-yard TD pass from McNair to Wilcox.
The Chargers answered with a 34-yard field goal by Nate Kaeding for a 10-7 lead.
Kaeding added a career-long 54-yarder late in the half but missed a 40-yarder in the third quarter, and a botched hold ruined a 52-yard try in the fourth quarter.
Scifres had a 71-yard punt in the fourth quarter. ... Baltimore G Edwin Mulitalo (elbow) left in the fourth quarter and did not return. ... Kaeding made 15 straight FG tries before missing from 40.