With 13 minutes left in Saturday’s game at Lavietes Pavilion, it seemed the Crimson would follow their usual path to victory. After a gritty, low-scoring first half, the hosts had exploded out of halftime to take a 14-point lead over Dartmouth. Surely the hosts would close out the game with suffocating defense, just as they had against Northeastern, against Boston University, and against the Big Green two weeks earlier.

This time, Dartmouth turned the tables. Over the next 10 minutes, the visitors reeled off an astounding 26-2 run, holding on for a 70-61 victory and the first upset of this Ivy League season.

According to Ken Pomeroy’s win probability calculator, Harvard had about a 98% chance to win when it led 43-29 in the second half. Several factors caused the Big Green’s comeback, their first victory over Harvard in six years:

Harvard’s energy lapsed at key points. Wesley Saunders had smothered leading scorer Alex Mitola throughout the first half, but when Malik Gill fell to the floor on a drive early in Dartmouth’s run, Saunders paused, perhaps expecting a traveling violation. A two-pass sequence found Mitola on the right wing, where he swished a three-pointer over Saunders’ late closeout. Later in the half, after a turnover in the paint, Gabas Maldunas beat all five Crimson players down the court for an uncontested, game-tying layup.

“They were playing harder,” Saunders said. “They were scrapping and fighting the whole game. We came out with a lot of energy to start the second half, but we couldn’t sustain it throughout.”

The Crimson’s lineup issues, a recurring theme this season, struck again. Harvard played the unproven Matt Brown and Chris Egi together midway through the half, then removed sharpshooter Corbin Miller with its offense sputtering, and finally finished the game with a four-guard lineup that has struggled this year. Even in the right situations, players came up short — Miller missed three open treys, and the team went 0-4 from the free-throw line during Dartmouth’s run.

“We’ve gone into offensive droughts, and that has hurt us,” Harvard coach Tommy Amaker said. “But we had opportunities to convert in transition … we had chances to finish around the rim. We didn’t do enough of what we needed to do.”

Most importantly, Dartmouth made the right adjustments. After coming off the bench and playing just nine minutes in the first half, Malik Gill was on the floor for the game’s final 16 minutes, giving the Big Green a spark on both ends.

Gill used his speed to disrupt Harvard’s defense: He notched a game-high six assists, and drove through a zone for a layup and one that fouled out Steve Moundou-Missi and gave Dartmouth the lead for good.  And he also used his notoriously quick hands: Twice tasked with defending Saunders in the post, the 5’9” guard poked the ball away both times, leading to run-outs for the Big Green.

Those plays were part of a larger Dartmouth strategy to mix up defensive looks, holding Harvard to 39% shooting and 18 turnovers. “If you let them run what they want to do on a consistent basis, it’s tough. They’re too talented and too well-coached,” Dartmouth coach Paul Cormier said. “But if we can sometimes have a little scatterbug like Malik, whose hands are always going … it’s a lot tougher.”

Dartmouth scored only 10 points in the first 12 minutes, thanks largely to Harvard’s fearsome interior defense. The Big Green made only one of their first nine shots from the post or restricted area; they finished the first half 4-14 there, but they started drawing fouls in the paint.

However, the Big Green were perfect at the basket in their second-half run, getting clean looks in transition and from offensive rebounds. Meanwhile, they also heated up from outside, including two Miles Wright three-pointers that capped the 26-2 spurt.

“We were able to get some turnovers and score off those turnovers,” Cormier said. “We didn’t have to run our offense all night against their very solid, five-on-five defense. They’re very tough to score on five-on-five, but tonight we were able to create some situations off our defense.”

Harvard isn’t panicking yet. Two games into a 14-game season is too early for that; besides, new Ivy favorite Yale nearly lost at home to shorthanded Brown at the same time as the Crimson went down. “We’re not discouraged. We know there’s still a lot of season to go,” Saunders said.

But there is no conference tournament in the Ivy League, and four of the last five champions have had two or fewer losses. That likely won’t happen this year; as Saturday’s results showed, there are no dominant teams, and the rest of the league has improved considerably. With four straight road games ahead, however — including trips to Princeton and Yale — the Crimson’s path to a fifth straight title looks much more difficult.