When it was announced Eli Manning would start for the New York Giants against Atlanta on Sunday, the Falcons quickly became 21/2-point favorites in a game that opened at pick ’em.

Ben Roethlisberger’s success aside, that’s the perception of rookie quarterbacks — they cost their team almost a field goal, especially when they have a leaky offensive line and are facing a good pass rush.

But Tom Coughlin made the switch in part because Kurt Warner has been tentative in the Giants’ last four games, three of them losses. Coughlin’s reasoning: Manning gets rid of the ball faster and is at the point where he’s comfortable with the system.

Both teams are like most of the league — unpredictable.

In losing three of four, the Giants were beaten by Detroit and Chicago at home and by Arizona on the road, all games they could have (some say “should have”) won. They won at Minnesota as an underdog.

The Falcons were beaten in Kansas City, 56-10, but came back the next week to win at Denver.

One more thing: The Giants have lost at home to Atlanta in each of the last two seasons, but Michael Vick was hurt both times.

Two years ago, Doug Johnson was the quarterback, last year it was Kurt Kittner. Johnson is now Tennessee’s third-stringer, and Kittner has been cut this year by the Falcons, Bengals, Giants, Patriots and Steelers.

Because neither Johnson nor Kittner is playing this week, and because New York’s offensive line — which has allowed 24 sacks in the last four games — will be cut en masse if it doesn’t protect the future of the franchise ….

GIANTS, 20-19

New England (minus 3) at Kansas City (Monday)

Another one of those Monday nighters that looked good on paper when it was scheduled.

The Patriots play fast and loose now that the burden of the streak is off.

PATRIOTS, 34-20

Indianapolis (minus 7) at Chicago

Lovie Smith should be a coach of the year candidate for winning three straight with Craig Krenzel at QB. But he doesn’t have Brian Urlacher on his side, and Peyton Manning plays for the other guys.

COLTS, 27-17

Pittsburgh (minus 41/2) at Cincinnati

The Steelers keep the hammer down.

STEELERS, 27-13

Washington (plus 101/2) at Philadelphia

The Redskins’ defense can control the Eagles to a point. But that Washington offense …

EAGLES, 23-6

Dallas (plus 8) at Baltimore

The way the Cowboys are playing defense, even the plodding Ravens’ offense can score.

RAVENS, 24-13

Green Bay (minus 3) at Houston

Another offensive challenge for the Texans, who have allowed 80 points in their last two games.

PACKERS, 34-27

Denver (minus 4) at New Orleans

Who knows with the Saints, but …

BRONCOS, 31-20

San Diego (minus-4) at Oakland

There’s no reason for a San Diego slide here.

CHARGERS, 37-27

Tennessee (off) at Jacksonville

David Garrard will be a big-time QB some day.

JAGUARS, 20-3

New York Jets (pick ’em) at Cleveland

No trick plays, Herman.

JETS, 22-20

Detroit (plus 71/2) at Minnesota

The Vikings’ losing streak ends here.

VIKINGS, 27-20

St. Louis (minus 1) at Buffalo

Remember that the Rams are the only team to lose to Miami.

BILLS, 24-20

Miami (plus 10) at Seattle

The Seahawks might be as unpredictable as the Rams. But they won’t lose to the Dolphins.

SEAHAWKS, 24-13

San Francisco (plus 8) at Tampa Bay

The 49ers are fighting for the No. 1 draft pick.

BUCS, 27-10

Arizona (off) at Carolina

“Off” is for Jake Delhomme. “Coach of the Year” is for Dennis Green if Cards make playoffs.

CARDINALS, 20-17

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LAST WEEK: 4-10 (spread), 8-6 (straight up)

SEASON: 71-71-2 (spread), 92-52 (straight up)