Chalmers' shot pulled Kansas into a tie after being down nine with 2:12 left.
"We got the ball in our most clutch player's hands, and he delivered," Kansas coach Bill Self said.
It was the first title for Kansas since 1988, when Danny Manning, now an assistant coach for the Jayhawks, led them to an upset of Oklahoma. And the shot earned Chalmers the most outstanding player honor.
"I had a good look at it," Chalmers said. "When it left my hands it felt like it was good, and it just went in."
The most memorable performance in this one came from freshman Derrick Rose of Memphis, who completely took over the game in the second half, scoring 14 of his team's 16 points during one stretch to lift the Tigers to a 60-51 lead with 2:12 left.
But Kansas (37-3) used the strategy any smart opponent of Memphis' would - fouling the heck out of one of the country's worst free-throw-shooting teams - and when Rose and Chris Douglas-Roberts combined to miss four of five over the last 1:12, it left the door open for KU.
Hustling the ball down the court with 10.8 seconds left and no timeouts, Sherron Collins handed off to Chalmers at the top of the 3-point line and Chalmers took the shot. It hit nothing but net and tied the score at 63.
Robert Dozier missed a desperation shot at the buzzer, and Rose went limping to the bench, favoring his right leg. Brandon Rush, Darrell Arthur and Darnell Jackson scored the first six points of overtime to put Kansas ahead 69-63. Memphis, clearly exhausted, didn't pull within three.
Arthur was dominant inside, finishing with 20 points and 10 rebounds, lots on dunks and easy lay-ups off lob passes. Chalmers finished with 18 points. Rush had 12 and Collins had 11 points, six assists and did a wonderful job shutting Rose for the first 28 minutes.
Rose wound up with 18 points in a game that showed how ready he is for the NBA. He was 3-for-4 from the line, however, and that one miss with 10.8 seconds left is what almost certainly would have sealed the game and given the Tigers (38-2) their first title.
Instead, the title goes back to Lawrence for the third time in the fabled program's history.
"If we played 10 times, it'd probably go five and five," Self said. "We got fortunate late."
The inventor of the game, James Naismith, was the first Jayhawks coach. It's the school that made household names of Wilt Chamberlain, Manning - and yes, even North Carolina's Roy Williams, the coach who famously left the Jayhawks, lost to them in the semifinals, but was, indeed, in the Kansas cheering section to watch Self bring the title back that he never could.
This game was not about coaches or sidestories, though. It was about the game, and what a dandy it was - a well-needed reprieve from a more-or-less blah tournament in which 42 of 63 games were decided by double digits.
This was the first overtime in the title game since 1997, when Arizona beat Kentucky 84-79.
Kansas, mostly Collins, put the clamps on Rose for the first half, allowing the freshman only four shots and leaving him spiking the ball on the floor as he walked to the locker room after a frustrating 20 minutes.
It stayed that way for the first five of the second half, but Kansas couldn't pull away. Douglas-Roberts made sure of it, winning enough of the 1-on-1 matchups that the Memphis offense creates to keep the Tigers in range.
Then, finally Rose took over - a 3-pointer here, a scooping layup for a three-point play next. Then, the capper, an off-balance, 18-foot shot off glass with the shot-clock buzzer sounding. It gave Memphis a 56-49 lead. Most teams would have been demoralized.
Clearly, Kansas is not like most teams.
In fact, the Jayhawks are a team that has come together in tragedy over the last several months. The deaths of friends and family of Jackson, Sasha Kaun and Rodrick Stewart all cast a bit of a pall over this team, making Jackson wonder at times if staying at Kansas was even worth it.
But it was an injury, not a tragedy, that might have been most responsible for blending this championship formula. Rush tore up his knee during a practice game last May, and his NBA plans were put on hiatus.
He worked his way back into shape this season and is playing his best right now. He didn't have the most impressive stat line of the night, but it hasn't all been about stats for him in this, his junior season. His defense was stellar, as usual, and surely his experience and resolve played into Kansas' refusal to go away.