Shai Gilgeous-Alexander scored 26 points to lead six Thunder players to score in double figures.
With their 12th straight win, Oklahoma City are off to the best start since the 2015-16 Golden State Warriors opened the season 21-0.
Reigning NBA Most Valuable Player Gilgeous-Alexander's 93rd straight game with at least 20 points is the second-longest such streak behind Wilt Chamberlain's 126 straight set from October 1961-January 1963.
He surpassed a 92-game streak set by Chamberlain from February 1963-March 1964.
Centre Chet Holmgren added 19 points, nine rebounds, three blocked shots and a steal for the Thunder, who opened the final period on an 8-0 scoring run to gain the upper hand in a tense clash that featured 15 lead changes.
OKC suffered their only defeat of the season against the Blazers on November 5, when the Thunder squandered a 22-point lead and fell 121-119 at Portland.
The Blazers again put them to the test, emerging from a back-and-forth first half with a 55-54 lead and taking an 87-85 lead into the final period.
Deni Avdija led the Trail Blazers with a triple-double of 31 points, 19 rebounds and 10 assists, but the Thunder wouldn't be denied.
Aaron Wiggins came up with a steal and a basket to launch the fourth-quarter opening burst. Holmgren produced a massive block then made a layup.
Jalen Williams threw down a dunk, Ajay Mitchell came up with another steal and a layup and suddenly the Thunder had a six-point lead less than two minutes into the final frame.
"(We) got a lot of turnovers in that stretch, which goes down to playing hard, being in the right spots, really cracking down on the game plan," said Williams, who played his second game since returning from off-season wrist surgery. "I think that kind of opened up the game.
"It gave us a lot more flow. Anytime you can get open layups in transition and offense, it just gives you more flow to the game, gives you more incentive to play defense, and we did that."
Portland cut the deficit to two with 2:58 remaining but the Thunder pulled away again.
Hawks top Sixers
The Atlanta Hawks beat the Philadelphia 76ers 142-134 in double-overtime to spoil Sixers big man Joel Embiid's return from a nine-game injury absence.
It was tied 132-132 with 2:44 left in the second overtime when Atlanta's Jalen Johnson drilled back-to-back three-pointers and the Hawks held on for a fourth victory in five games.
Johnson led the Hawks with 41 points and 14 rebounds and Nickeil Alexander-Walker added 34 points.
Tyrese Maxey scored 44 for Philadelphia, including a basket to force overtime, and Embiid added 18 points in his first game since November 8.
Boston's Payton Pritchard scored 42 points and Jaylen Brown delivered his fourth career triple-double with 19 points, 12 rebounds and 11 assists as the Celtics edged the Cavaliers 117-115 in Cleveland.
Pritchard scored six points in the last 90 seconds to help Boston hold off a late charge by Cleveland, who were led by 27 points from Evan Mobley with 21 from Darius Garland and 18 from Donovan Mitchell.
The Minnesota Timberwolves, fuelled by 32 points from Anthony Edwards, beat San Antonio 125-112, out-scoring the Spurs 36-19 in the fourth quarter to post their second win in as many days after rallying to beat the Celtics.
De'Aaron Fox scored 25 points and Devin Vassell and Keldon Johnson added 22 points apiece for the Spurs, who were again without injured superstar Victor Wembanyama.
Lakers top Pelicans
In Los Angeles, Luka Doncic scored 34 points, pulled down 12 rebounds and handed out seven assists as the Lakers beat the New Orleans Pelicans 133-121 despite the absence of LeBron James, who was sidelined with a foot injury.
Austin Reaves added 33 points for the Lakers, who scored 46 in the first quarter and never trailed.
The New York Knicks were also buoyed by a big opening quarter, putting up 41 in the first in a 116-94 win over the Toronto Raptors.
The Knicks saw a 24-point lead sliced to three midway through the third period before they steadied the ship to claim a fourth straight victory.
Karl-Anthony Towns led the way with 22 points and Josh Hart added 20 points and 12 rebounds.