Luka Doncic wasn't about to let a sprained ankle slow him down, nailing a game-winning three-pointer at the buzzer to lift the Dallas Mavericks to a 135-133 overtime playoff win over the Los Angeles Clippers on Sunday.

The 21-year old Slovenian phenom, who was playing with a tender ankle and missing his offensive sidekick Kristaps Porzingis, finished with 43 points, 17 rebounds and 13 assists to level the first-round NBA Western Conference ­playoff series at two games each.

"This game was from another planet," said Mavericks coach Rick Carlisle of Doncic's heroics.

Doncic made a basket with 50 seconds left to tie the score 130-130 then gave Dallas a two-point lead with a spinning move to the basket with 19 seconds remaining.

He capped his triple-double with a 27-foot step-back jumper from the left side as time ticked down, sparking a wild celebration on the floor in the NBA's quarantine bubble in Orlando, Florida.

"I can't explain the emotions I had when I saw the ball go in," Doncic said. "When I saw the whole team coming towards me that was one of the best feelings I have ever had as a player."

While Dallas levelled their series, Boston became the first team to reach the second round with a 110-106 victory over the Philadelphia 76ers.

Kemba Walker scored 32 points and Jayson Tatum added 28 and 15 rebounds for the Celtics, who swept the Eastern Conference first-round series 4-0.

Doncic, who is playing in his first NBA playoffs, carried the Mavericks Sunday without Porzingis, who was a late scratch because of a knee injury.

But the pre-game buzz was all about Doncic's health, not Porzingis. Doncic sprained his left ankle in the second half of game three and had an MRI on Saturday to determine the extent of the damage.

"This morning I wasn't feeling good but as soon as I stepped on the court I knew I could go," said Doncic, who recorded his second straight triple-double.

Trey Burke added 25 points, Tim Hardaway scored 21 and Seth Curry chipped in 15 points for Dallas, who led by 12 with nine minutes remaining in the fourth quarter.

Lou Williams had 36 points and Kawhi Leonard finished with 32 for the Clippers, who blew a 21-point first-half lead.

Game 5 is on Tuesday.

Meanwhile, the Celtics' Walker, who arrived in Boston after eight seasons of frustration with the Charlotte Hornets, was basking in his first NBA playoff series win.

"It feels good," Walker said but added, "The work's not done. We won a series, but we're still looking forward to some more tough ones."