"I was just taking what the defense was giving me," Cartwright said. "They put a lot of pressure on Zack and a lot of focus was on him. I tried to attack the basket and take advantage of the open looks I got."
The sophomore guard had just 12 combined points in the Quakers' first two games, shooting 5 for 17.
"The last two games, I thought all those other shots were going in, too," Cartwright said. "Fortunately, most of them went in tonight."
After tying the game with a driving layup with 37 seconds left in regulation, Cartwright scored the Quakers' first five points in overtime, including an acrobatic layup on a three-point play that put Penn up, 64-62, with 3 minutes, 54 seconds left. The Quakers never trailed again.
Rider had a chance to win in regulation, but Jonathon Thompson's eight-footer from the baseline fell short with two seconds left.
It got a little scary for Penn, which looked in control and led, 74-67, with just more than one minute left.
Cartwright missed a pair of free throws with 52 seconds remaining and Jeff Jones nailed a three on the Broncs' ensuing possession to pull Rider within two, 74-72, with 41 seconds left.
But Cartwright made up for it as he made a pair of free throws with 34 seconds left to give Penn a 76-72 advantage.
Rosen, who scored 53 points in the Quakers' first two games, was scoreless in a foul-plagued first half when he didn't attempt a shot in 14 minutes.
But the talented senior point guard, who is the reigning co-Ivy player of the week and a returning all-Big 5 performer, came to life after the break and ended by making 6 of 9 field-goal attempts and all six of his free throws.
"I appreciated the patience and poise he had," head coach Jerome Allen said of Rosen. "He wasn't pressed. He just allowed the game to come to him. His maturity and overall IQ is a plus."
"He didn't want his opportunity to shoot the ball to supersede what was best for the team."
Add senior wing Tyler Bernardini, who had 14 points, to the Rosen/Cartwright partnership, and the Quakers can play with anybody's backcourt.
Daniel Stewart had a team-high 26 points, and Jones added 19 for the winless Broncs (0-4), who are off to their worst start in 15 years.