The Thunder rolled past the playoff-bound Dallas Mavericks - who rested Luka Doncic and Kyrie Irving among others - 135-86 to emerge from the trio of teams who went into the final day of action tied atop the West.
It marked the first time that three teams entered their final games with identical records, all with a shot at the number one seed in a conference.
Thanks to the Thunder's edge in their head-to-head record, the Nuggets' 126-111 victory over the Grizzlies in Memphis wasn't enough and the Minnesota Timberwolves, who also had a chance, fell 125-106 to the Phoenix Suns.
The Suns snatched the sixth and final automatic playoff berth and will face the No. 3 Timberwolves again in the first round.
In New Orleans, superstar LeBron James scored 28 points with 11 rebounds and 17 assists in his 112th career triple-double to propel the Los Angeles Lakers to a 124-108 victory over the Pelicans and eighth place in the West.
The defeat dropped the Pelicans out of sixth place and they'll host the Lakers in the play-in tournament on Tuesday, with the winner advancing to the playoffs as the seventh seed.
James added five steals and Anthony Davis had 30 points and 11 rebounds against his former team. Davis gave Lakers fans a scare when he hobbled out in pain late in the fourth quarter, but coach Darvin Ham said he believed it was muscle spasms and not an injury that might sideline Davis in the post-season.
James' triple-double was his fifth this season and his playmaking helped spearhead a dominant performance in the paint, where Los Angeles outscored New Orleans 68-42.
The Golden State Warriors, with Stephen Curry and Draymond Green resting niggling injuries, beat the Utah Jazz 123-116 to lock up the last play-in berth.
They'll play Tuesday against the Sacramento Kings, who cruised past Portland 121-85, with the winner of that play-in game earning a shot at the loser of the Lakers-Pelicans contest for the final Western Conference playoff berth.
All 30 teams were in action on the final day of the regular season, and 12 of the 15 games had playoff implications.
Brunson propels Knicks to No. 2
There was a bit less to settle in the East but the New York Knicks, fueled by 40 points from Jalen Brunson, edged the Chicago Bulls 120-119 in overtime to grab the second seed.
Brunson's pull-up shot with 1:01 remaining in regulation tied it at 109-109.
Brunson fed Donte DiVincenzo for a go-ahead three-pointer with 3:13 left in overtime and the Knicks held on for their 50th win of the season.
The Knicks leapfrogged into second place over the Milwaukee Bucks, who fell 113-88 to the Orlando Magic as Bucks star Giannis Antetokounmpo missed a third straight game with a leg injury.
The Magic, led by 26 points and 11 rebounds from Paolo Banchero, avoided the play-in tournament, clinching the fifth seed ahead of the Indiana Pacers.
The Pacers grabbed the sixth and final automatic playoff spot with an emphatic 157-115 victory over the Atlanta Hawks and booked a first-round clash with the Bucks.
The Boston Celtics, already assured of the top seed in the East, closed the regular season with a 64th victory, 132-122 over the Washington Wizards.
The Cleveland Cavaliers, who also had a shot at second place, fell to the Charlotte Hornets 120-110 and finished fourth. They will meet the Magic in the first round.
The Miami Heat, beaten by the Nuggets in last year's Finals, finished eighth after a 118-103 victory over the Toronto Raptors.
On Wednesday, the Heat will take on the Philadelphia 76ers, who rested star big man Joel Embiid in a 107-86 victory over the Brooklyn Nets - in the play-in.
The winner will advance to the playoffs and the loser will take on the winner of the play-in clash between Chicago and 10th-seeded Atlanta.
