Deadlocked at 118-118 with a "target score" of 120 to win, Miami edged Memphis when Larsson drove to the hoop and sank a 10-foot jumper over Scotty Pippen Jr that bounced three times off the rim before dropping through the hoop for the victory.
"Pelle set the tone for us," said Heat player development coach Dan Bisaccio. "That's what you want from one of your draft picks, to come right in and dominate on both sides of the ball."
Heat forward Josh Christopher scored 24 points, shooting 6-of-10 from 3-point range, to lead the Heat and win Summer League finals Most Valuable Player honors at the Thomas & Mack Center in Las Vegas.
The event provides an off-season showcase for new and young NBA players, with scouts from all teams analyzing talent.
Miami center Kel'el Ware had 21 points and 10 rebounds while Alondes Williams had 21 points and Cole Swider added 19, hitting 5-of-8 from 3-point range.
"These guys deserve all the credit," Bisaccio said. "They worked so hard from day one. I'm so proud of them."
Larsson, the 44th overall pick of last month's NBA Draft by Houston taken for the Heat as part of a deal, hit 7-of-9 shots for 16 points, none bigger than his last.
"Coach drew up a great play that we've run before in practice a bunch of times," Larsson said. "They did a good job guarding it. I knew me and Kel'el in pick and roll was pretty dangerous.
"We had shooters everywhere so they didn't want to help (defensively) and I just made it."
Jake LaRavia scored a game-high 32 points to lead Memphis while Pippen, the son of six-time NBA champion Scottie Pippen, added 29 points and 11 assists and G.G. Jackson added 28 points on 11-of-16 shooting for the Grizzlies.
Swider sank a 3-pointer with 19.6 seconds remaining in regulation to put Miami ahead, but Jackson answered with a 3-pointer to pull Memphis level at 113-113.
"Cole hitting that shot was big for us," Larsson said.
After a Miami turnover, Pippen missed a 3-pointer at the buzzer to force overtime, with special "target score" rules in place so the first team to reach 120 points would win.
A Christopher 3-pointer lifted Miami to 118 but LaRabia answered with a corner 3-pointer to equalize, setting up the closing drama as Miami took a first Summer League crown.
The NBA All-Summer League First Team included Pippen and Jackson of Memphis, Miami's Ware, Houston's Reed Sheppard and Jordan Miller of the Los Angeles Clippers.
Brooklyn's Jalen Wilson was named the Summer League overall Most Valuable Player after averaging 21.8 points over five games.
