The 20-year-old Doncic grabbed rebound No. 17 with just over a minute left in the third quarter to set a new career mark -- and picked up No. 18 about 30 seconds later -- then watched from the bench as Dallas reserves finished off a comfortable 118-97 victory over the New Orleans Pelicans.
"I felt like the ball was just coming to my hands after they missed," Doncic said. "I didn't even know I had 18. I went back and saw it on the big board. I didn't even know."
Doncic finished with 33 points, and with those 18 rebounds, he became just the third player to put up that stat line before his 21st birthday, joining Shaquille O'Neal, who achieved it with the Orlando Magic in 1992-93, and John Drew, who reached it three times with the Atlanta Hawks in 1973-74, according to Elias Sports Bureau research.
Doncic, along with fellow starters Kristaps Porzingis and Tim Hardaway Jr., didn't play after the third quarter. Seth Curry took over from there, scoring 12 fourth-quarter points as the Mavericks outscored New Orleans 34-22 in the final frame.
In the third quarter alone, Doncic had 15 points and 10 rebounds. He's the only guard to hit that mark in a single quarter in the past 20 seasons.
"It was great," Mavericks coach Rick Carlisle said. "Eighteen rebounds is a lot. That's a lot of rebounds for a point guard. I don't care what planet you're from. That's tremendous."
Doncic played just 28 minutes, giving him his third game with at least 30 points in under 30 minutes. That's the most for a player before turning 21 in NBA history, according to ESPN Stats & Information research. No other player has multiple such games.
All of this came on a day when Doncic was named the Western Conference Player of the Month.
"Every award means something to me, especially this one," Doncic said. "It's a big thing for me, it motivates me. The team helped me, the team, the coaches. Without them, I couldn't have won."
Doncic became the second player under the age of 21 to score at least 600 points in his first 20 games of the season, joining LeBron James, who accomplished the feat in 2005-06. Both players had exactly 614 points, according to ESPN Stats & Info research.