This Saturday’s Harvard-Penn game could have been the biggest of the year, another de facto Ivy League Championship Game in a long line of them. But then the Quakers played the fourth quarter last week.

Penn had jumped out to a 16-0 lead over Princeton at Franklin Field and held a lead midway through the third quarter. Then the Tigers pounced. The Quakers’ 23-17 advantage turned into a 24-23 deficit, and then a 31-23 hole. Princeton’s defense held Penn to 41 fourth-quarter yards while the visitors pulled away from the defending Ivy champions, 38-26.

The loss was Penn’s (4-4, 3-2 Ivy) first to Princeton (7-1, 5-0 Ivy) since 2006.

The Tigers have quickly gone from pretender (1-9 in 2011), to contender (3rd in the Ivy League in 2012), to undisputed king. It shouldn’t be that easy.

Turnarounds are supposed to take time. It’s supposed to be a long, painful process. But evidently Princeton coach Bob Surace found the cheat code, the shortcut from the basement to the penthouse so he did not have to climb the stairs.

Either Harvard or Penn has won at least a share of the last six Ivy League titles. The Tigers appear poised to change that this season.

And that makes this Harvard-Penn matchup different. Instead of Google vs. Apple, it’s Yahoo! Vs. Bing. Or maybe Saturday’s squads are more like AOL and Myspace, trying to stay relevant after years of success.

Rather than a fight for supremacy, Saturday will bring a struggle for survival. The winners will not be celebrating, they will be hoping.

And regardless of the outcome, Penn will also be worn out. A week after falling in front of 21,000+ fans at homecoming, the Quakers are playing the most important game of their year for a second straight week.

Meanwhile, Harvard is coming off a laugher against Columbia, except it wasn’t funny. The Crimson cruised to a 34-0 win as Harvard coach Tim Murphy rested everyone who had so much as a scraped knee.

Will what amounted to a bye week against the Lions be enough to help the Crimson beat Penn and stay alive in the title hunt? I guess you’ll have to read on…

PENN AT HARVARD (7-1, 4-1 IVY)

It’s hard to believe the defending-champion Quakers are now tied for third in the league. But there’s a good chance they finish even worse than that. Despite returning a number of key players from last year’s team, Penn has lost two Ivy games by a combined 39 points. 2013 could turn into the Quakers’ worst year in quite a while, or they could rally, beat Harvard this week, blow out a winless Cornell next week, and finish a respectable 5-2 in the league. I think the former is much more likely.

PICK: Harvard 31, Penn 20

DARTMOUTH (4-4, 3-2 Ivy) AT BROWN (5-3, 2-3 Ivy)