The French star, who again came off the bench as the Spurs ease him back into action in the wake of a knee injury, scored 16 of his 21 points in the second half, adding six rebounds and three blocked shots.
"My mindset was just, I have to close out the game," Wembanyama said of his pivotal jumpers, adding that the victory showed the Spurs' character.
"It felt like they were playing better basketball than us, but we stayed in there," he said.
De'Aaron Fox scored 21 points for San Antonio and Keldon Johnson added 18 points and 10 rebounds as the Spurs kicked off a three-game road trip with victory in the clash of East and West second-placed teams.
Derrick White scored 29 points and grabbed nine rebounds and Jaylen Brown added 27 points, eight rebounds and seven assists for Boston.
In Detroit, the Los Angeles Clippers erased a double-digit deficit to hand the Eastern Conference-leading Pistons a 98-92 defeat.
Kawhi Leonard scored 26 points and John Collins added 25 for the Clippers, who trailed by as many as 19 in the first half and were down 14 early in the fourth quarter.
Collins made a pair of free throws to give the Clippers a 93-92 lead with two minutes remaining and James Harden fed Ivica Zubac for a dunk and the Clippers held on for the win.
They out-scored the Pistons 30-16 in the fourth quarter, Detroit coughing up 12 of their 25 turnovers in the final frame.
Duncan Robinson scored 20 points to lead the Pistons, who were without key contributors Cade Cunningham, Jalen Duren and Tobias Harris as well as ailing Isaiah Stewart.
Elsewhere, Donovan Mitchell scored 28 points and passed off eight assists to spark the Cleveland Cavaliers over Minnesota 146-134.
Two nights after losing at Minnesota, the Cavs also had 24 points on 11-of-16 shooting from Evan Mobley and 23 points off the bench from Jaylon Tyson to rally past the Timberwolves.
"They got up 12 and we responded, did what we had to do and got the win," Mitchell said, noting the improvements from Thursday's loss.
"We made adjustments," he said. "We locked in, dialed in and did a good job. We kept our foot on the gas, they made some runs, and we continued like always."
Darius Garland added 22 points for Cleveland while Sam Merrill contributed 20 points, hitting 5-of-6 three-point shots, and Jarrett Allen had 16 points and 11 rebounds.
Anthony Edwards led Minnesota with 25 points while Julius Randle had 22 and reserve Naz Reid contributed 23, hitting 5-of-6 three-point attempts.
The Cavaliers improved to 22-18, sixth in the Eastern Conference, while the T-Wolves slid to 25-14, fourth in the Western Conference.
