It would be a big upset, but . . .

Old-time bettors must get a good laugh when people claim that a victory by the New York Giants over the undefeated New England Patriots would be the biggest upset in Super Bowl history.

Although a ton of attention has been given to the Patriots’ double-digit point spread for next Sunday’s game, a Giants’ win would not come close to the impact that the New York Jets’ 16-7 victory over the Baltimore Colts had in Super Bowl III in 1969.

Back then, the NFL and AFL still played separate schedules and the Colts were regarded as one of pro football’s most dominant franchises.

From 1958 to 1969, Baltimore won three NFL championships and played in the league title game four times, which included a 34-0 blowout win at Cleveland that earned the Colts a berth in Super Bowl III.

Oddsmakers made Baltimore the overwhelming favorite with most sportsbooks listing the Jets as 18-point underdogs.

Their reasoning was simple: New York was the third-best team in the inferior AFL, which already had two top teams (Kansas City and Green Bay) overmatched by Green Bay in Super Bowls I and II.

So when the Jets upset the Colts, the victory not only shocked the betting world, it also rocked the pro football landscape. That’s why a win by the Giants would be impressive but not the greatest upset in the history of the Super Bowl.

“Later-year Super Bowl point spreads have been inclined to be inflated [and] the Colts were favored by [18],” said point-spread guru RJ Bell of Pregame.com. “With a smaller percentage of casual bettors, that line would have not been inflated near as much, so it’s very safe to say that the quality margin between the Colts-Jets was much wider than this year’s matchup.”

After New England opened the week as a 13 1/2 -point favorite, the line quickly dropped to 12 as a result of heavy money dropped on the Giants, who have won three playoff games in a row as road underdogs.

And although the Patriots are 18-0, they enter the Super Bowl on a point-spread slide, having failed to cover the line in seven of their last eight games.

But New England supporters have reason to be confident based on the history of previous big spreads in the Super Bowl.

Of the nine teams that have been favored by 12 points or more, six have won and covered the spread.

The largest line covered in the Super Bowl? In 1995, San Francisco was favored by 18 points over San Diego in Super Bowl XXIX and the 49ers covered with a 49-26 win.

As of Saturday afternoon, the Giants still dominated in betting support. According to Wagerline.com, New York had received 63.2% of the picks against the spread (1,375-800), and TheSpread.com’s betting chart had the Giants getting 68% of the action.

Pro Hockey

The NHL All-Star game will take place today and the most intriguing bet will be the over/under for goals scored, with the total listed at 16, according to Sportsbetting.com.

There were 21 goals scored in last year’s game, a 12-9 Western Conference victory.

lonnie.white@latimes.com